Welcome to the world of 04.5, sometimes it's a nightmare. When polaris went to the newer style front end they did it mid year wich only caused headaches for everyone that bought a late model. Whenever you buy parts bring that model number that starts with AO. If your dealer is a good dealer they will be able to tell the difference in parts that you will need. Some of the differences are;

04.5 has a straight up and down shift pattern
04 has a sort of upside down h shift pattern

04.5 has a different instrument cluster with digital readouts

04.5 has the newer style roller cage front 4X4 system (crap... my.02$)

As for the override, that is only used in reverse. When you back up the machine has a built in rev limiter for safety. By pressing and holding the overide button it by passes the rev limiter and alows 4X4 in reverse.

I think there are some other differences I just can't think of them right now. There are threads on this topic, do a search and you should find them.