This one's a tough one. Looking at the amount of rust on that item, you'll want to remove as much rust as possible to stabilize the relic...on the other hand you want to leave the plating.
Electrolysis is definitely out.
So I'd most likely use EvapoRust (available at most auto stores). There is a post in "Cleaning and Preservation" by me on how to use the product, with photos of the results.
Now, I do know that the product won't react with the plating (the only thing it reacts with is rust). But I don't know if there might be rust underneath that plating, which would mean that the plating would be gone anyhow after cleaning. And of course, if you left it as-is, it would rust away anyhow.
So I'd try that first.
The only other option is to heat the relic (rust and all) in the oven, and then take it out with an oven mitt and coat it generously with crisco to try and slow the rusting process.
It's "either/or"--because EvapoRust will not work after you Crisco a relic.
Best Wishes,
Buckleboy