I have a bath/shower with separate hot and cold water valves and a third one that is a diverter to switch between the shower and the tub faucet. Recently I had a steady dripping from the faucet so I changed the stem washer. I also tried to change the valve seat, but apparently I ended up stripping the seat as the square hole became rounded and I was no longer able to remove it.

I called a professional to look at it and he was also unable to remove the seat. He indicate the only option was to replace all three handles with a single handle and either tile over the holes or use a conversion kit with a plate that covers the holes. He wanted to use a Symmons conversion kit. My understanding is that apparently it is against code to have separate hot and cold valves these days in order to protect from scalding.

My questions are:
1. Is there no option to have 3 separate handles/valves in any form? I really prefer this older look and would like to preserve it if at all possible.

2. Is there any way to remove the broken/stripped seat? The plumber indicated he could try an E-Z out, but the ones he had were too short. If I could find one that was about 5 inches long (to reach all the way into where the seat was) that I could try that, but there was no guarantee it would work.

My apologies if I have used ay incorrect terminology.

Thanks for any suggestions or help you can offer.