Is it possible to substitute a piano finger from, say right hand thumb to left hand thumb?
Dorico doesn’t have a built-in way to do this at present, no. I guess the notation would be something like R1-L1?
Hmmm. Good question. I tried to use “-1” in the left hand, but there was no note to select, and a Dorico didn’t like the leading dash in another case. Anyway, maybe the right hand has “1-“ to guide the reader. Dorico doesn’t like the trailing dash.
I tried finding examples on line but have struck out so far.
You could create a custom playing technique for that particular case.