Work in Progress!!!!
WARNING: This is the most crucial step of these whole instructions. Compared to a GoPro or Action 4 the front display of the Action 5 Pro is very brittle and breaks easily. There are multiple methods to remove such a front screen. However we did not have luck with any of that. Using much heat results in a non reversible heat damaged display. Using solvents to break up the glue will result in visible spots on the display. Using much pressure to pry the display out will result in micro cracks and a broken screen. Also the electronics are not protected on the backside so by pressing it out you will risk damaging the electronics. Dremeling the display out using a rotary tool will leave lots of plastic on the front screen that is hard to remove without cracking the display.
The approach we took takes a lot of time and work, is also not 100% bulletproof but we had the best experiences doing it like this. If you have found a better method please let us know. Also don't rush with this process. It takes a good hour to get the display out safely.
For safety its recommended to wear safety googles for the risk of tools breaking and also use some cutproof gloves. You can easily slip on the rubber/plastic and cut yourself. So always be mindful of your finger / hand position.