An open source tweak that help end-users can paired your own Apple Watch on new watchOS version with old iOS
So feel free to use it. There's no risk or any chance that cause damage to your iPhone or Apple Watch. You can even restore your newer backup of your Apple Watch without any restriction (tested). But be careful about your data lost, I'm not respone for that. That app basically hook somes function in NanoRegistry.framework to make "Plugins" like PingMySupport,...
Hopefully version 1.1 can help download app from AppStore... I'm not tested yet.