The oil pan plug teeth on your 93 civic si are worn out can you just change the plug or do you have to replace the pan?

You have two choices, as far as I know. If you want to do it right, the only way is to change out the oil pan (sorry). The other fix is a repair plug from an auto parts store. It includes a rubber thimble-shaped plug that you insert into the pan first and then the steel plug that screws into the plug. The steep plug expands the rubber insert into the stripped pan threads to create a seal.

I've never used one, so I don't know how well they work. Another option I just thought of, if you want to remove the pan but don't want to replace it, is to weld up the old plug and then install a new threaded drain next to it. I bought one from B&M for a transmission pan once. You cut a new hole and then install the threaded plug assembly.

Best solution, of course, is to replace the pan.

Good luck!