DanG writes:

Other than that, what can they do?

It's the government brute squad. Unlimited resources to take your life,
liberty, or property, as they see fit.

Don't think they won't. Building codes and permits are chiefly about
boosting the profits of a few tradesmen via barriers to entry and restraint
of trade, so the code/permits/licensing goons tend to have powerful
enforcement when they are roused by a cheeky homeowner.

Although Florida has a law guaranteeing her citizens the right to work on
their own domicile within codes and permits but without a trade license,
I've stood in the Broward County building department and listened as the
chief plumbing inspector said a guy with three engineering degrees wasn't
allowed to replace an ordinary kitchen faucet in his own home.

Your friend should either submit fully to these authorities, or hire a
construction lawyer to contest anything unfair.