Yeah it's okay to do and smart to pratice on. If you have a scrap yard near by you could buy a panel that has some dent to it so they are not going to use it. That way you can get different defects and paints to work on. Or better if they have a panel for your mothers car you get familier with that paint when practice.
The problem with polishing rock chips is you get polish in them that are white or the color of the polish. You can do so you don't dabb where the rock chips at worst. And work with the polisher with from the area near to the area with rc and back up and down again. Then have ipa or a panel wipe product at hand and wipe it off before it's drying.
If you are able to get a scrap yard panel. Have fun and test the limits. Get some wet sanding paper p1500 p3000 p4000 to simulate damage on the paint.
