I wouldn't use anything too sharp, as it would be very easy to go too far and punch through the Ensolite.
I don't remember if I mentioned it in my thread but I'm using a brake adjustment tool (that's what I had around when I started this job, and it turned out that it worked good enough for me).
The ends are not very sharp, it's a bit like the end of a flat screwdriver. You could still poke through the Ensolite if not careful, but it's nothing like a chisel or cutting blade.
At some point on my trailer the window frame was behind the upper galley cabinet, my brake tool wasn't long enough to reach the corner of the window, so I simply "sharpened" the end of a paint
stir stick that I as able to slide behind the cabinet, between the wood frame and the Ensolite, and that worked good. So it can be a very low tech tool! (a big toe nail would probably work!!
If you don't have a lot of silicone to remove and clean off, ungluing the Ensolite is the hardest part. Sometimes I was able to peel it off easily, sometimes it was still glued hard, even if the wood under was badly rotten. Pretty good glue they used...