Making a backup of %APPDATA%\IDMComp\UltraCompare or compressing this directory into an archive file is not enough by default because of UltraCompare stores the configuration settings in Windows registry by default up to version 20.00. At Configuration - Application Layout is checked the setting Use registry for settings (not INI file) by default up to UC v20.00 while this setting is not checked by default in configuration of UltraEdit and UEStudio. The default for this setting changed with UC v20.10. This configuration setting is not checked anymore by default on starting UC v20.10 and there is no configuration from a previous version of UltraCompare.

So it is necessary to run from within a Windows command prompt window the following command to backup also the configuration settings stored in Windows registry:

%SystemRoot%\System32\reg.exe EXPORT "HKCU\Software\IDM Computer Solutions\UltraCompare Pro" "%APPDATA%\IDMComp\UltraCompare\uc_settings_pro.reg"

Then the entire registry key of UltraCompare Professional with all subkeys and all values is written into the file uc_settings_pro.reg in application data directory of UltraCompare.

The restore is done by running the following two commands:

%SystemRoot%\System32\reg.exe DELETE "HKCU\Software\IDM Computer Solutions\UltraCompare Pro" /f
%SystemRoot%\System32\reg.exe IMPORT "%APPDATA%\IDMComp\UltraCompare\uc_settings_pro.reg"

I recommend to export the registry key also on having not checked the setting Use registry for settings (not INI file) as a few settings are always stored in Windows registry like the Explorer shell integration configuration.

There should be exported also the registry key HKCU\BCGWorkspace on existing depending on configuration to use or not use an INI file for the settings. The workspace settings are stored by default in a subkey of registry key HKCU\Software\IDM Computer Solutions\UltraCompare Pro, but there is the possibility depending on configuration that the workspace settings are stored and read by mistake to/from this registry key. An error message is output on export and no *.reg file is created on this registry key not existing at all as in most configurations up to UltraCompare Professional v20.00.

The issue with the workspace settings (theme, toolbars, etc.) is that on unchecking the configuration setting Use registry for settings (not INI file) the workspace settings are stored neither in %APPDATA%\IDMComp\UltraCompare\uc.ini nor in a different file in application data directory of UltraCompare nor in Windows registry under key HKCU\Software\IDM Computer Solutions\UltraCompare Pro\UltraCompare Professional\BCGWorkspace like on having checked this configuration setting as by default on using UltraCompare up to v20.00.

The workspace settings are stored in Windows registry under key HKCU\BCGWorkspace with all other settings stored in uc.ini with the exception of the shell integration settings for the DLLs. That is a bug in code of UltraCompare which I reported years ago and on which I sent a reminder from time to time to get it fixed. It was fixed finally with UltraCompare for Windows v20.20 as it can be read below.

All keys and values are kept in registry on unchecking in configuration Use registry for settings (not INI file) and so most people do not recognize that the workspace settings are stored under wrong key. But I have deleted entire registry key HKCU\Software\IDM Computer Solutions\UltraCompare Pro after unchecking the setting and exiting UltraCompare and so could see what UltraCompare creates on next start with the configuration settings and histories stored in uc.ini. There is not much recreated on next start. There is suddenly a registry key tree replicating the storage location of uc.ini. I don't know the purpose of this registry key tree, but I suppose this key tree is not created intentionally, but is caused by a bug in code which was fixed finally with UltraCompare for Windows v20.10. And the wrong storage location of the workspace settings is most likely also caused by a bug in code, most likely a missing initialization of the registry key under which the workspace settings should be stored with most other configuration settings stored in uc.ini.

So you know now why your theme changed on unchecking Use registry for settings (not INI file). The reason is the (initialization) bug in code of UltraCompare.

UltraEdit and UEStudio don't have this bug. The workspace settings are stored by default in the appropriate files (*.in0 and *.rb0 or *.vod depending on version).

Note: The shell integration settings are stored in uc.ini and in Windows registry on unchecked setting Use registry for settings (not INI file). The DLLs loaded by Windows Explorer read the settings always from registry and never from an INI file. That is also the case for the settings of the shell extension DLLs of UltraEdit and UEStudio.

The default behavior for storing settings changed with UltraCompare for Windows v20.10. The configuration setting Use registry for settings (not INI file) is no longer checked by default to save the configuration settings into the files:

1. %APPDATA%\IDMComp\UltraCompare\uc.ini
2. %APPDATA%\IDMComp\UltraCompare\volatile\uc.vod

The registry key HKCU\BCGWorkspace is still created and used by UltraCompare for Windows v20.10.

The issue with replicating the storage location of uc.ini in Windows registry under key HKCU\Software\IDM Computer Solutions\UltraCompare Pro is fixed with UltraCompare for Windows v20.10.

These changes on settings storage are done in preparation for Cloud Services support which was introduced with UltraCompare for Windows v20.20.

UltraCompare for Windows v20.20 stores and loads the workspace data in/from file %APPDATA%\IDMComp\UltraCompare\volatile\uc.vod and deletes completely on first start after upgrade also the registry key HKCU\BCGWorkspace. There are only a few registry keys and values stored by default under the registry keys UltraCompare and UltraCompare Pro under the registry key HKCU\Software\IDM Computer Solutions which are mainly for the UC installer and the UC Explorer shell extensions.

Users of at least v20.20 of UltraCompare for Windows installed on Windows 10 with support for Cloud Services and with access to a cloud storage can backup the UltraCompare settings now on cloud storage and restore them from there.

All other users of UltraCompare for Windows v20.20 or any later version need to run the following two command lines in a command prompt window to first export the few registry keys and values of UltraCompare Professional into two registry files and then backup entire folder %APPDATA%\IDMComp\UltraCompare by copying this folder to another folder or compressing the entire folder into an archive file while no instance of UltraCompare is running.

%SystemRoot%\System32\reg.exe EXPORT "HKCU\Software\IDM Computer Solutions\UltraCompare" "%APPDATA%\IDMComp\UltraCompare\uc_settings.reg"
%SystemRoot%\System32\reg.exe EXPORT "HKCU\Software\IDM Computer Solutions\UltraCompare Pro" "%APPDATA%\IDMComp\UltraCompare\uc_settings_pro.reg"

A restore of the manually saved settings is done by first deleting folder %APPDATA%\IDMComp\UltraCompare, then restoring this folder from the folder copy or the archive file and running next the following four command lines in a command prompt window.

%SystemRoot%\System32\reg.exe DELETE "HKCU\Software\IDM Computer Solutions\UltraCompare" /f
%SystemRoot%\System32\reg.exe DELETE "HKCU\Software\IDM Computer Solutions\UltraCompare Pro" /f
%SystemRoot%\System32\reg.exe IMPORT "%APPDATA%\IDMComp\UltraCompare\uc_settings.reg"
%SystemRoot%\System32\reg.exe IMPORT "%APPDATA%\IDMComp\UltraCompare\uc_settings_pro.reg"