As you can already toggle VBlank timing through playback compatibility settings, I don't see much of a reason to have a global flag for this - VBlank modules are a tiny fraction of all 4-channel MODs and I'd rather have autodetection of these modules be as accurate as possible. You are probably thinking about this problem from a listener's perspective, but adding such a global option to a tracker may give the impression to authors composing MOD files that writing VBlank modules is a legitimately useful thing to do, but it really isn't - it will just create even more confusion because suddenly there are people that expect that their newly-written modules sound correct in all MOD players.

When using the libopenmpt, there is no way to force the vblank (or at least, I couldn't find any).

Okay, libopenmpt is a completely different topic (and should have been mentioned in the initial report). This essentially makes this a duplicate of issue 0000779.