I have replaced panel guts with like parts, as in same maker and line. I did one just recently, because the BC-type 100a main breaker and bus burned.
The new 125a panel had main lugs, but was otherwise identical to the original panel's guts, even to the notch for the old panel's factory hold-down kit.
Everything fit and lined up, including the new cover, I didn't waste the customer's money swapping the cans, and I didn't damage any of the old wires.
Replace the inside with what? :grin: I believe Cutler hammer will custom make the guts for any brand panel. The can of a panel is just that so there should be no issue with a new door and guts.