Rather than using heat to re-attach the covering a thin mist of windex under the monocote will also hold it down. Mist on the windex and place the patch on the plane, Sqeechie out the excess windex with a credit card and let sit over night. the next day you can use trim solvent to secure the edges permanently. Also if there are any wrinkles a warm hot iron will take them out. As far as removing the decal I would be careful you are liable to end up with a bigger hole, but I agree it needs to be removed for the patch area.
Good luck with your repair.
Alan