Hey, Jellybeam,
Why not just leave the rosin on -- it's part of the history and patina of the fiddle.
When browsing old fiddles at instrument auctions -- usually unstrung, so I don't get a chance to hear them -- I'm always led to bid on the ones that are caked with old rosin. Dem's the ones that have been PLAYED!

If experimenting with cleaners, and you're not sure what the original finish is, always go for a hidden spot to try it out -- under the fingerboard, for instance.

Good luck, Rob