Yes, it is possible. There are even multiple methods available. Which versions are we talking about?

Note: Some features need registration in Windows registry and can be therefore used only for one version, best the later one. These features are the Explorer integration and the FTP, SSH, telnet support.

Okay, I suppose on home computer is installed already UltraEdit v24.10 and additionally UltraEdit v18.20 show be also used as on office computer.

The following steps are in this case necessary to use both versions parallel within same or with different user accounts.

1. Copying program files of UltraEdit 18.20.
   
   Copy entire directory %ProgramFiles(x86)%\IDM Computer Solutions\UltraEdit from office computer to %ProgramFiles(x86)%\IDM Computer Solutions\UltraEdit18 on home computer.
   Please note the modification of directory name on home computer by appending 18 to name.
   
2. Copying configuration files of UltraEdit 18.20.
   
   Copy entire directory %APPDATA%\IDMComp\UltraEdit from office computer to %APPDATA%\IDMComp\UltraEdit18 on home computer.
   Please note again the modification of directory name on home computer by appending 18 to name.
   
3. Correct paths in configuration files.
   
   Start UltraEdit 24.10, open file %APPDATA%\IDMComp\UltraEdit18\uedit32.ini, replace all occurrences of %APPDATA%\IDMComp\UltraEdit with %APPDATA% (environment variable reference) in search string replaced by real path from office computer by real path of %APPDATA%\IDMComp\UltraEdit18 from home computer, save the modified INI file of UltraEdit 18.20 and exit UltraEdit 24.10.
   
4. Create special shortcut for UltraEdit 18.20.
   
   Right click on Windows desktop, and click in context submenu New on menu item Shortcut. Browse to %ProgramFiles(x86)%\IDM Computer Solutions\UltraEdit18\uedit32.exe, click on OK and Next, enter as name for the shortcut UltraEdit18 and press key Return or click on Finish.
   
   Right click on shortcut UltraEdit18 and left click in context menu on last menu item Properties. Append on Target a space character and the string /fni /i="%APPDATA%\IDMComp\UltraEdit18" with keeping the environment variable reference as Windows automatically expands it before starting uedit32.exe.
   
   Click on button Change Icon and select third instead of first icon which helps to better identify that this shortcut is for UltraEdit v18.20. Click two times on button OK to save the changes on shortcut file.
   
   Note: /fni is the option to force new iinstance which overrides an unchecked configuration setting Allow multiple instances. And /i="..." specifies a specific INI file to use instead of the standard INI file whose name depends on name of executable. Most configuration files are loaded/stored in directory of INI file which makes it possible to use multiple versions of UltraEdit parallel.
   
5. Register and configure UltraEdit 18.20.
   
   Double click with left mouse button on shortcut UltraEdit18 to start it. It must be most likely first registered because of UE 18.20 stores the license activation data different to UE 24.10. In case of license activation was done successfully and UE 18.20 exited, start UE 18.20 again using shortcut UltraEdit18.
   
   Then open Advanced - Configuration - File Associations and make sure the setting Integrate with Explorer as is unchecked. Navigate in tree to Application Layout - Miscellaneous and make sure the setting Automatically check for updates is unchecked too.
   
   Save and close the configuration of UltraEdit 18.20 with a click on button OK and exit UltraEdit 18.20 or let it running.
   
6. Start UltraEdit 24.10, open Advanced - Configuration - File Associations and check Integrate with Explorer as if you want to use the shell integration in Windows Explorer.
   
   Note: I don't have Integrate with Explorer as checked as I don't need this feature because of using Total Commander as file manager with UltraEdit fully integrated in TC per configuration. And I have not tested if shell integration with using two versions of UltraEdit parallel causes any problem.

That's it. By default currently latest installed UltraEdit is used on starting UltraEdit. But UltraEdit 18.20 is started on using shortcut UltraEdit18. Both versions can be used at same time and it does not matter in which order both versions are started. But never start UltraEdit 18.20 with a different method than using the shortcut with the two additional parameters.

don_bradman wrote:That's a lot of work.

Not, it isn't. It takes just 1-2 minutes to really do it when knowing what to do. It takes 5-10 minutes to read and do it. And it took more than 30 minutes to write the steps well formatted so that hopefully really everybody can do it.

It is of course easier on using 2 different user accounts as in this case it is possible to install first older version of UltraEdit with advanced option to install UltraEdit only for current user and next install newer UltraEdit with another user account again using advanced option to install only for current user. But in practice using 2 Windows user accounts to have 2 UltraEdit versions installed is not as handy as it is on having both versions available and running parallel, especially on the requirement to test complex regular expressions, macros or scripts in both versions of UltraEdit quickly.

There are even more possibilities to use multiple versions on same machine with same user account. This is just the one which I thought is most useful for your requirements of parallel testing Perl regular expressions and scripts after reading all your forum topics.