I dont know for sure, but it looks like rolas is an intransitive verb, you can just say "The actor performs." Here you are clarifying the intransitive verb with the "by manner of" correlative. The sentence wouldnt make sense if there was an extra subject with no clause, and rolas cant take the accusative. Unless theres a suffix that turns intransitive verbs transitive, which there probably is, but that doesnt make this sentence with Kiel any less valid. You can generally word most things multiple ways.
I'm not asking about the Esperanto sentence; I'm asking whether the English sentence "The actor plays a judge" would be acceptable as a translation of "La aktoro rolas kiel juĝisto" - not a word-for-word translation but nevertheless one that is reasonable English and conveys the same meaning.
You may be placing them in the wrong place in your mouth for rolling them. Turns out, there's a lot of different tongue placements in the mouth, and different ways to roll them, and there's a lot of advice about how to develop a rolled R on the Internet. One cute trick is to say butter butter butter over and over again, faster and faster.
Being a native English speaker, I've always rolled my r's by putting the tip of my tongue lightly on the alveolar ridge (right behind the top teeth) and exhaling. If it helps, try exhaling with your tongue in a neutral position, then moving it upward. Do it quickly though, you have to release a lot of air.
That means something different. "As if he were". I suppose in a sense that's what actors do, perform as if they were someone else, but I think "kvazaŭ" is more suited to a sentence such as, "That teacher is acting as if he were a guard" (Tiu instruisto agas kvazaŭ li estus gardisto). Of course, acting in that sentence = behaving, not doing what actors do!