Welcome to the forum, perfect place for this question.
@neil_w ‘s solution should work. The only problem I see is if you can’t get the old mount out (and if it doesn’t come out easy, don’t force it) that residual hardened piece of elastic may stick out where you cut it and snag your chute. You may need a file or rasp to file it down smooth.
Executioner is a pretty rocket, so going with a replaced internal mount will give you the best cosmetic result and the best aerodynamic result. If you just want to fly it and are not too concerned about looks, you can poke a hole about midway down the body with a needle, place a loop of Kevlar around the rocket, thread the Kevlar through the hole and out the front. Put a piece of tape around the loop around the rocket (I use Mylar, it’s shiny and says, “Yeah, I meant to do that!”). I’ve never been a fan of the trifold mounts, I want the inside of my rocket to have a smooth uninterrupted contour so the chute and wadding come out unimpeded.
that said,
@kevindcornwell posted this trick for smooth flat trifold mounts
The OP referred to a common problem, that of a ragged trifold snagging a chute. I've used the balloon clamp method with excellent results - a perfectly smooth and flat trifold every time. Insert a small party balloon into the tube so the balloon end is below the trifold (may need an long balloon used in making balloon animals). Blow it up - it will press the trifold firmly into the tube, the pressure will ensure an even distribution of glue, and the balloon will peel right off when you pop it the next morning.
stolen from this thread, post 17
https://www.rocketryforum.com/threa...rd-trifold-mount-with-a-better-system.155646/
straight trails!