[friagram]

you could always use onentitycreated and find tf_projectile_sentryrocket (or whatever it's called) and edit it's velocity down to your desired amount
I was going to do this at one point...
Like -> if engineer has wrangler -> and engineer fires rocket -> and engineer is aiming at bad guy -> make rockets homing + critical on said enemy.
Would be lolz.
Same concept, different application.