If it’s on paintwork, I spray with a waterless wash to soften up and use a detailing brush. These work well and have a handy rubber end for cracks and crevasses....
A thought is to use gtechnic panel wipe. It's solvents is very a like as in polishes. And sometimes you can have luck that the same desolves with the same kind of product. I would not take a polisher on it if I was not certain of getting all off that has been able to stuck on the old compound. If the wash you useing softening it up maybe it can be polished off. But I would do it with more amount of polish than useally. You could apply the polish on a small section and then gently wipe it off after dwelling some time both by hand. The aggitations a polisher does is extreme compared to be wiping or lightly aggitate it with a brush. That's what I would be afraid of if makeing an even more mess than necessary.
Pro grade compounds and polishes are water soluble - so getting the car really wet and washing it or scrubbing the body panels should loosen and remove the old compound. Time is your friend, that is letting water do it's thing - soaking into the compound and softening it.
Anything not removed from washing will come off when you compound or even polish the paint.