What is this called and can I paint it?
 

Oh the typical rear window trim rot.

Unfortunately to remove that piece you need to remove the window. But you're in luck, we have (had?) a body shop guy on the forum and he fixed his problem:

https://blazerforum.com/forum/builds-48/how-paint-your-rear-window-trim-2-door-pics-37860/

oktain, I love you. (no homo)

s'ok, it's bro-mance lmfao.

Good luck! And I'd suggest painting it black since red is a difficult colour to match.

Yeah after reading the thread I might just throw some bedliner on lol.

I did mine not too long ago. Not hard to do. Just take your time and be patient. Remember to cover/protect everything really good so you can fix the trim rot spots with no damage to painted areas. It costs me less than $50.00 in materials from an auto paint supplier and a Saturday's worth of time. I probably did over kill on the masking off the rest of the vehicle from dust and overspray. It only looks intimidating.

Up to you, the body filler is more for filling the holes in. And you could probably sand some of the plastic too.

Paint
 

Sorry to bring up an old thread. I tried some do it yourself work using some 150 grit sand paper and 4 coats of higher end rustoleum spray paint. Came out nice but we will see how it goes with durability.
http://i345.photobucket.com/albums/p.../Photo0075.jpg
Pretty good for some rattle can