Two version are definitely required, unless you use the Tweaker. The Weaker is suppoed to allow you to switch the MS Store files to the Steam version location for use there quickly to allow it to be done with one install, but if you don't use the Tweaker, you have to use double the storage space, since you would need to log-in to the MS Store version to get the code (it has to be fully updated) and then input the code in the Steam version (which also needs fully updated) It is impossible to just do something like this:
- Install on Windows Store
- Update the client to latest version
- Launch client and issue 15 minute time limit code
- Uninstall MS Store version
- Install PSO2 on Steam
- Patch the client to latest version
- Time is up and code can't be entered and must start back at Step 1.
The reason for this is, the client will have a 60+GB patch to download from SEGA, rather than MS Store or Steam. If you have the proper permissions, though, you should theoretically be able to download the Steam version client and just not update it. Then, after completing Step 3 above, close the MS Store version, go to where the game files are and move them to the Steam folder (not copy, it has to be moved or cut and pasted), then run the Steam version and have it check the files and replace the altered config files, log in and enter the code. Depending on if the hard drive is SSD or not, it might be able to move all the files and check them all fast enough to where you can still enter the code within 15 minutes. However, as stated, the only way to guarantee to have enough time to enter the transfer code is two have double the space to have both installed at once. This is easier if you have two hard drives, though, and use Steam on the second hard drive and the MS Store version on the main hard drive.