Is макарони really the general word for pasta or does it refer to the specific kind of pasta called macaroni?
It's a both a general term for pasta and the word for what we call macaroni in English. If you wanna see the different kinds of pasta, the Ukrainian Wikipedia is a good place to look.
So do only feminine words with endings "a", "я" etc. change in Accusative case? I am confused that макарони does not change at all