I just did a set of rims, stripped them down to aluminum, sanded them and had them powder coated silver. Looks good, but there sure is a lot of crevices and corners to clean by hand. Took many applications of stripper and some scrubbing with an assortment of wire and brass brushes to get it all.
If the clear coat is in good shape and not separating and/or has cancer working under the clear coat, you can lightly sand the clear coat and put a coat of paint right on top, no reason why not.
If you use a stripper, really wash them well when your done, aluminum is porous and some of the stripper might stay in the pores. I have a coupe of small flaws in mine, that are probably due to not washing them one more time, with a mild soap and hot water, before the acid dip prior to the powder coat.
If I ever do it again, I´m gonna find some kind of mild acid and/or pickling solution to treat the rims before sending them in for powder coat. The uncleaned areas (left over clear coat) will probably show up well, when the rim is pickled a light mat grey.
Cleaning the stripper, all the way off, is probably the most important part.