I actually just put my Pearce extensions on my Gen 4 27 today. I was having one heck of a time getting my base plates off as well. The YouTube vids didn't help me at all. I ended up having to use a 'C' clamp shaped vise grip to pinch the mag together so the stops that prevented the factory base plate from coming off would be pushed in enough for me to get it released. Once that was done I pushed in the spring with a smaller screwdriver and it popped right off.
You need to muscle the darned thing off, no doubt about that. I wear leather work gloves and use a stainless steel pin punch with a large shaft, and prop the magazine tube on my workbench (with a coupla rags to keep if from scratching).
I used Pearce +2's on all my mags, in fact just installed 2 today. Remember: you really gotta force that sucker out!
Suggestion: don't use a c-clamp, the metal liner can be permanently deformed. Just a thought.
I'm trying to add Pearce "Plus Zero"grip extensions. The YouTube videos only seem to show installation on thinner bottomed magazines. The thicker base plate on the G36 magazines does not want to come off. I know some force is needed but I'm worried about breaking the plastic. I will consider this advice and try again today.
FWIW, I've done it on over a dozen magazines and it works. The "poke the lock plate in and push forward with the punch" works, might have to brace the magazine on something, and I've used all my might on it without breaking the magazine or the magazine buttplate, either removing the stock ones or removing the aftermarket ones after installation.
I was able to get the Pearce +zero grip extensions onto my Glock 36 magazines. I'm over 200lbs and had to drop my weight into it with needle nose pliers. I tried several times with an Allen Wrench, but that was not enough leverage. Don't be afraid to break the plastic. Also, have your thumb handy to prevent the spring etc. from taking out your eye.