I didn't see it on the rules or the forum, so I ask myself:

Which is the general rule in the line-ups on compilations? Add the band members in the time when the compilation was released or add the band members who have participed in any of the songs on the tracklist?

Add the band members who are credited with performing on the album, denote which tracks if necessary. Simply adding members based on who was in the band at the time of the release is inaccurate if they didn't perform on it, so I would avoid that if you aren't familiar with the band/own the release.

Should we even add members to compilations? Maybe lineups should be disabled for compilations.

That idea sounds nice. What about compilations of previously unreleased songs? Would it still be a workable solution even if it's the band's only release?

There could be a checkbox for veterans to enable line-ups for compilations.

I feel that this if the most suitable form to do in those cases, but i would also agree and give the support to eliminate the line-up on the compilation albums, and to add a little description in the additional notes if new songs are released in that album...

Add the lineup to the additional notes?

Only if the compilations really deserves to have a lineup added, like a compilations of previously unreleased songs.