I had a similar issue trying to change a tank over from Tough 2000 V1.1 to V2: How to transition material version in a Form 4 tank
My workaround was to clip a small clamp to the top cap of my empty bottle so it weighed the same as a partially full bottle (be careful opening the lid if you do this - I kept hitting the clamp because I forgot it was attached). You still need to wait ages for the slow filling warnings to appear and eventually allow you to start printing despite slow filling being detected.
I think the logic that formlabs has is that you would just open a new bottle. We are printing regularly at the moment, so I don’t worry about resin sitting in the tank for extended periods but perhaps that’s what’s a concern for you? Perhaps if you share the reason for not opening a new bottle it might help identify a different solution.