Patina is mostly a chemical reaction between the metal of the
mod and something else. The part that is not a chemical reaction is dirt.
When you clear coat something you keep other stuff, like air, out so the patina will not change. If you want to change the outer layer of metal on the
mod you need to strip the clear coat off so you can get to it.
Removing the coat depends on what it is. Some come off with chemicals and others are a lot harder to remove. The one sure way to get rid of anything is mechanical. the problem with this is that getting into the engraved areas is hard and will likely wear away part of the engraving.
Once you have the clear coat off you can do several things. One is nothing and let a natural patina develop over time. The other is to force a patina with chemicals. Ther best instructions I have found are from craft people forcing a patina on some other copper thing. Use Google and look for copper patina or force patina.
Most patinas are softer than the metal so they will change as you use them. If you want it to remain unchanging then you will have to coat it. Use something you can get off easily because the coating is real soft and it will scratch and you will have to take it off and redo it. Again the craft people are best at this and you can find them with Google.
