re: Painting with wood method or alternatively patches packet

Clever one Mike. The only things I can think of right off are that the packet may not be as rigid as you would like and masking tape gums up blades a little when you cut it. Will veneer tape not work on the tar paper?
The purpose is to keep the veneer piece in exact position and for that it should work so I’m betting it works.
Like I said, clever.