One shot only means, that you can use the rocket just one time. When it's gone, it's gone. But you can arm your Razorwing with up to four rockets (e.g. 4 Monoscythe OR 4 Necrotoxin OR 2 Mono and 2 Necro).
Search in the forum for the tactic guides written by Plastikente. You will discover some more gems like the soultrap/ huskblade combo.