Q1) Is there a way to force Dorico to accept extra notes in a bar — essentially allowing overfilling a measure beyond the time signature, like you can in some other notation software?
Q2) Also, is there a “Rebar” function similar to what Finale offers, where the music can be re-measured automatically after changes?
So add the notes as whatever tuplet value you need, and then hide the bracket and number in the Properties panel. (Can’t believe I’m faster than @charles_piano with a tuplet-related answer here.)
Could you elaborate a bit more about why you need this? I used it regularly in Finale but I haven’t had any need for it in the past year with Dorico (and your question just made me realize that!).