Keeping the default Keep All Versions option selected will not adversely affect your backups.
As for changing the bucket’s lifecycle, I too would assume that it does not affect your backups. Any sensible implementation would either
- Stop versioning from this point forward but keep previous versions or more likely
- Remove all old versions of files but keep the current versions.
Since neither of these would have any effects on current files, which are the only ones duplicati cares about, you should be fine. But just to note again, this is based on an assumption.
You could verify B2’s behaviour in a separate bucket. Or you could just leave everything as is. Since you have already set duplicati to keep unlimited backups, there should be very little unwanted data in your bucket (deleted by duplicati, but versioned by B2).