Back in the day (Mid-80'*), I recharged my own R-12 system from time to time on the '68 Ford XL I had then. It worked fine for me. I don't think I really started to have a lot of trouble with the system until I moved to Florida, and tried to get the system working again after a prolonged period when it had been disconnected and open to the atmosphere. I basically had to replace EVERYTHING, and spent a lot of $ on it, and put the 'new' 134a in it.
When I went out to California some months later to collect my large travel trailer, one of the refrigerant hoses came off of the condenser... it never had AC again... because I never wanted to go through the hassle again.
I can say that I did have very good luck converting/charging a 1987 Volvo 240DL I owned briefly last year with R134a. It looked like the AC had been repaired shortly before I got it, but it was down on coolant. Getting it charged was a royal pain because of where the service port was, but I had cool air the last part of the summer, until the head gasket went...
If you put the new parts on you mentioned, have a shop evac and leak test the system, then you should not have any problem refilling it with R12 or doing a conversion right then and there yourself. Just be sure to add the right kind and amount of lubricating oil, and if it is not with R12, you'll also be out of luck because you can't mix ANY of the R12 and R134a. (Except, I probably did that in my Volvo as it hadn't been converted when I got it. And it worked GREAT anyway!
Still, potential fines shouldn't be dealt with lightly. You'll have to find out, is there any controlling legal authority?
Just don't run for public office if any one is privy to your environmental indiscretion.