This is the easiest way to interop unlock Lumia 950, 950XL since it can't be done with interop tools
1. Download the following
2. Extract the iutool.7zip
3. Extract the acer.service.acersystemservice.spkg to "C:\acer"
4. Install the vcreg appx and dependencies in developer mode
5. Connect the Lumia to PC and copy the NdtkSvc.dll and newndtksvc.dll to the Documents folder in internal storage
6. Open command prompt as administrator and type:
"iutool.exe -v -p C:\acer" the phone should reboot to gears. If not manually reboot
You should see the gears.
8. Go to step 2 in vcreg app and follow the prompts. It will ask to reboot device couple of times
You can install interop tools appxbundle from here for some tweaks.