Yes. Assuming your bumper trim had plastic primer applied to any bare plastic, and then you just applied either a different (colour) primer and/or aerosol paint. Plastic primer is essential to help the paint stick to the plastic. You can put whatever other primer/colour on top of it.
Smooth down whatever paint you applied with 400~600 grade wet and dry, tack the b'Jesus out of it to remove all the dust, then put one more coat of the colour on it. Clear coat adheres best to fresh (<48 hours old paint). If you get any paint runs, let the paint dry, cut it out with 400-600 and then re-spray that section with colour again until you're happy with the surface coverage on he whole piece. Don't cut or polish the "final" finish.
Within 48 hours, apply the clear coat. You're presumably going to be using an aerosol with the two-part/activator can. Shake it until you can't stand up any more, to mix it thoroughly. Use light coats but don't let each coat dry completely in between coats.. add some more while it's still just about tacky.
The 2-pack aerosol are supposed to last about a week once activated.. but try to get the top-coat coverage finished in one go, in case the top-coat starts to harden or the nozzle clogs etc. I doubt you really want to buy another aerosol just because you missed a bit.
Let the clear harden for a few days.. ignore any runs or bugs in it... When it's completely dried (probably one week later if you're not in a rush) then sand it down with 1200~1500 grit (very wet)... to get an even matt finish... then polish it using an abrasive polish.
Don't overdo it.. if you see colour on the polishing mop/cloth, then you've broken through the clear layer.. but if that happens, the good news is that at least you'll know what you're going to be doing for the next two weekends..
Ralf S.