Provisionals on veneer preparations can be challenging. The “shrink to fit” or “shrink-wrap” technique has gained popularity over the years. That is, provisionals are fabricated and trimmed on the teeth without being removed and are left until the seat day. I know great clinicians who use this technique but I am insecure with it.
Consider fabricating your provisionals prior to making your final impression. If you place a piece of braided 000 cord into the sulcus prior to fabricating the provisional you can get excellent margin capture.
By removing the provisional and trimming it outside the mouth you don't have to worry about damaging a margin on your preparation or creating unnecessary sensitivity around the margins by inadvertently cutting into cementum while trimming.
You have the added benefit of being able to measure the thickness of my provisionals before making impressions. If the provisional is thinner than you want your final veneer to be, then you have the chance the make the corrections to the prep before the impression, thereby avoiding having to redo the impression.