I did exactly what you said. It wasn't as stuck as I thought.
The reason you aren't supposed to re-use copper gaskets is that they work harden. Once they've been torqued down the become harder and hence don't conform and seal. I deal with it in vacuum systems all the time. Can you get away with reusing?Sure sometimes. If it's something that's hard to take apart I don't usually chance it unless I have to. This seems to fit that category.