MuseScore 3.2.3 Portable

Thank you for the tip, but I tried it and I am not sure it is the right approach:
with this Custom.nsh (and QtKeysCleanup in the .ini file) after closing MuseScorePortable the keys I listed in [QtKeysCleanup] section are wiped, even if they already existed before launching MuseScorePortable.
On the other hand, by using the backup/restore approach (as it is now in Development test 2) those keys are reverted back to how they were before launching MuseScorePortable (for example, empty if they were originally empty. Moreover, on relaunching MuseScorePortable they are restored. For example, I can save a custom color in the color selection menu and it is kept from one session of MuseScorePortable to the next, or the file open dialog remembers the recently visited locations from one session to the next; and another application using Qt 5 will not have its Qt file dialog and custom color preferences overwritten (probably unless launched at the same time when MuseScorePortable is running, but such a preference mess in that situation would happen also in the Custom.nsh/QtKeysCleanup case).

So, unless it can give additional problems, that at the moment I can't see, I think I will leave the handling of these specific Qt registry keys as done for Development test 2. Please correct me if I am wrong and/or such application registry behavior could be problematic; I am definitely not an expert in registry handling and I may overlook something important.

Here it is: https://github.com/AntonioBL/MuseScore/commit/3ec781e0dff55ba7be56fd4b48...
I didn't trigger a new Appveyor build on the official MuseScore account to avoid clogging the disk space available on Appveyor, but simply repacked the old build with the new .ini file. If only modifications to the Launcher files are required, a full new build is not needed.
I am not sure what happens first: the text replace or the registry backup/restore of stored values.