99% solved, final resume:
As usual, there where different issues, complementing each other - from the software and from me …
the current user has no admin-rights, so there is the usual problem of admin versus user
there was the 32bit of NP++ installed; the update to 64bit did not reset all registry-settings of 32bit
I checked the HKLM-settings and thought that this will overwrite the user-settings: my fault, existing user settings stayed alive
there where user settings for “.re” which linked to “re_auto_file” which linked to inactive x86-start-commands
Now I cleaned up all x86-values to current links, and this enabled the command “Open with … - select Standard application …” again. Now a double-click on .VVA and .RE opens it with NP++
The last “1% cosmetic unsolved” for both file types is that the icon in Explorer is smaller than the standard icon and the file-description is not “Notepad++ Document”.
Thanks to all posters for advice!