Sure, the easiest way to add a carrier, is to create a .prd route for both sides and add a US Task force to the .mis file!
I have made a manual, how to make it: http://www.lowengrin.com/download.php?view.139
But it could be then, that DCG creates for the japanese only missions against the aircraft carrier and probably ignore the enemy ground units at Guadalcanal!
The other problem are the US destroyers in the .srd route! If they would destroyed during a mission, then it could be, that they will spawned into the .prd route and the trooptransports have no more escorts!