Yes, the little silicon caps on the end of RIC hearing aid wires are called domes. Domes from many hearing aid manufacturers are interchangeable. Just find the ones that fit your ear canals and give you the right sound. The ones I use, Widex large tulip domes for my Phonak P90 HAs, are classed as vented domes. There are open, vented and closed domes in a variety of shapes and sizes. A crude rule of thumb is:-
Open domes will give you the most ambient sound and least bass.
Vented domes will increase occlusion and increase bass.
Closed domes will be the most occlusive and give the most bass response.
My own experience is primarily concerned with keeping the domes in my ear canals without them backing out within minutes of wearing, a point which most audioligists i have come across don’t seem to regard as that important, or something that is easily resloved.
You can tweak your audi’s fitting to your heart’s content with DIY fitting but for me the key to good sound quality is getting the right domes.