Think Twice...Cut Once!

Chances are the vertical fin rests on, and is glued to, the horizontal stabilizer. The part of the fuselage near the tail that comes up from the stab and curves over to the fin, might be more for aerodynamics and looks, rather than strength (Although I cant be certain without having the model in front of me).

If this is true, then I suggest cutting enough of the plastic fuselage away in order to perform a good glue job to secure the fin to the stab.

A repair of the newly created "access slot" can be done by gluing a piece of material over the breach.

Pay very close attention to the WEIGHT of all materials used on this repair, in order to avoid adding a ton of weight up front in order to regain balance.

After the repair is complete, check the balance. Good Luck