Strictly speaking you’ll need to go back for an adjustment if you’ve changed the venting. However, as most of the effect is below 1Khz you’re not really going to suffer that much unless you either start getting more feedback (more venting) OR too much LF gain (Less venting).
Further increasing venting my give you a ‘thinner’ sound experience overall as you lose the LF ‘warmth’ from the signal and you may start to lose some of the speech clarity too: which might be more apparent to others around you.