Been away for a while from this thread 

If you own a Windows 10 Mobile device, you are good to go. Follow these steps in order to get your device ready.
1. Head to Settings > Update & Recovery and tap on “For Developers“
2. You will find three options here. Choose the second one which lets you sideload apps from other sources.
3. Next, transfer/copy the appx file of the app to your Phone/SD Card storage.
4. Browse to the file via File Explorer, tap on the file and it will throw an install prompt.
5. If you really want to give it a try, tap Install else tap cancel.
6. If all goes well, you will find the app under the app list under 20 sec.

this information is available via here .. try with your own risk ya

As far as I understand nope this is not rooting the phone like Android though. The options to set "For Developers" are there available. However as usual do it at your own risk ya.

You can always restore back to original ROM via "Windows Device Recovery Tool"

P/S: Support paid app lar hahaha since Windows 10 Mobile community already so small lol