Can regular gas go into a 2002 Acura RSX type S?

yes you could, but there is a down side to that it will ping in really heavy load or driving the car hard because of the tremedusly high compression that's why Honda tells you to use 91 its best for the engine

Answer

yes when i bought my rsx from Honda (used) they filled it with 87 octane but ever since ive been using 91 again.

Answer

The engine control system uses a knock sensor to control ignition timing. Low octane fuel results in pretty severe ignition retard, mine would not rev over 4000rpm on regular fuel, no knocking or pinging was evident, but neither was the normal performance this engine delivers. Compression ratio is 11:1 and high miles and carbon build up may increase this further.