couple of cents... and i guess i will work from back to front. the clear cant be in the paint. it defeats the point. with two stage paints, the paint is flat and since metal flake is disc shaped and can stand on edge and so on, it makes it impossible to sand or buff without ruining the finish, hence the clear over it to make the different stages of polishing possible.
when a finish can be sanded and polished, its a single stage paint such as lacquer was. it can look good when applied right but isnt as durable over the long haul. its easy to scuff your clear with fine grade paper and reclear or customize but with a single stage all you can do is repaint.
as for adhesion promoter, if you are using a modern two stage system, in most cases adhesion promoters are unnessary, with proper prep work, being sure to remove all grease and contaminants, then rinse clean, then sand most items with about a 600 grit, then use a good prep cleaner (wearing rubber gloves to avoid getting skin oils in contact and thereby avoiding fisheyes in your paint) you wont have any problems getting paint to stick to your item. if it was something pliable like vinyl then i can see the usage but most plastics are rigid enough that the small amount they flex makes both promoter and flex additive not necessary. on the other hand if you arent completely sure, the promoter cant hurt.
as for pearl, you wont get a good pearl coat out of a rattlecan. you can try a bottle with one of those aerosol tops for spraying reduced paint, but as was correctly said, it will most likely clog the tip and in a best case where it doesnt, it will probably spit and sputter and mess your finish up. if you dont have the equipment necessary to do the paint work or have a buddy that can, its usually worth it to do the prep yourself and get a local body shop to just spray it for you. it might cost you 60 to 100 bucks but the hassle saved will be well worth it.
even a small touch up gun or air brush wont emulate correctly the factory sprayed finish, the tip size and proximity of spray will cause it to come out differently to say nothing of factors such as temperature and humidity.
on a final note, dont forget about paint fade. as parts are exposed to weather and sun, the finish slowly but inevitably fades, but usually does so evenly and so slowly you dont notice until compared to fresh paint. best to have the paint color matched to what you have instead of buying the correct paint so you dont end up with part of your ride not matching.
sorry its so long but i hope i helped or maybe cleared up a thing or two, if not, i tried. if anyone has any questions, feel free to ask, i would be happy to offer what i know.

 

Kind of where I was at with it Shadetree Prez. I couldn't figure out how they'd get two-stage into one can, but hey, I'm not a paint chemist either. Unless it's pretty basic like a Vivid Black, it is really tough to paint small "add-on" pieces and have them match up to the factory finish. I'd like to see how they come out if they try the aerosol can.