I'm a captain grade 1 in Halo 3, can i get my highest skill to 30 to rank...

[Nico H]

...up to major? I'll do that instead of get the EXP.

 

[Dragon]

Yes you can, try doing lone wolves until you get your highest skill up to 30. Or you can do what really annoying people do and quit right after the game starts and get the smae effect.