I'm sure you could do this easily yourself by going into the script for the item and editing the fire delay. You can usually look at the various different function names to get an idea of what they do. For some practice, maybe try editing the gun?
It may also help to note that the Homing Rocket may be best used more as a 'utility' than a full-on weapon due to that same 'OP' quality. Maybe just make it rare?