Binds are kept in files called .cfg. You can use the /exec cfgname.cfg to quickly load up a bind set.
You'll want to make a new .cfg called "marauder.cfg". Bind "/exec marauder.cfg" to 0, for example.. In this .cfg, you'll want something like
/evolve class3adv
/bind mouse2 +attack
etc
etc
etc
(COMMANDS SHOWN ABOVE ARE NOT THE REAL COMMANDS)
Then, whenever you press 0, assuming you have enough evos, you'll evolve into an advanced marauder and your mouse buttons will be rebound.
Using this system, you can have complicated binds for both teams. For example, I used to have my binds configured so I could join a team with the push of a button, and depending on what team I joined my say_team binds were different and my binds for upgrades were different, too.