clear spray paint will seal it up and keep it from getting worse but it will give the rust a glossy cover. Clear does come in a variety of finishes: crystal, gloss, matt, flat, lacquer, etc.. One key to using clear is don't use very much if you don't want it show. It's real easy to use too much. I've used clear on pitted chrome rims and I didn't like the results.
I usually use car wax (turtle wax) on all bike parts and frames but turtle wax dries kinda white on rust. You just can't get it to polish on rough surfaces.
I've car rehab shows where they just spray all kinds of clear over rusty body panels to try to halt the rusting process. it is a particular look that some like.