Can you change a single rocker arm on a 1991 Prelude 2 liter Si or do you have to change the whole assembly?

Anwer. If I am understanding your question correctly, yes you can but to get to the one rocker you have to get to it by removing the dual cams together. It is connected in a cradle like assembly connected to two cam gears(one for intake and one for exhaust). At this time would be a great idea to do a timing belt change that way it will be something less to worry about down the line.