Do you mean physically modifying a printer you bought from Bambu, and selling that on? Potentially as a service, where you buy in bulk and re-sell with this modification? If so, I don't see how that would change anything about the software you're allowed to run on it.

Or do you mean manufacturing your own printer that is a copy of theirs with 10mm extra build volume in each direction, and with your own software? That may be illegal if they have any patents, but otherwise should probably be ok, and would of course not have anything to do with their software - but you still couldn't take the software from one of their printers and running it on yours, most likely.