Much of Xcode is wonderful to use in my opinion. You can dig and dig and dig and still find new things in there. However, there are aspects that induce sphincter tightening just thinking about it (without version control). Anything you do to a project file is scary stuff.
Recently I had a project that I attempted to add a watchOS complication to. You can’t undo that. I ended up with a bunch of extra targets, including a new watch extension itself. I wasn’t sure what I was doing and things started producing warnings and errors. I deleted a bunch of stuff and cleaned the build folder. Whew.
Turns out, it’s quite easy to create a new project with complications present before anything. Most of the project’s code was able to be ported quite easily. Some other things took some time (plist files, user interfaces, etc.)
I have yet to find out how to add a complication to an existing watchOS application. I spent too much time searching the internet for answers. I was actually able to mostly figure out complication templates too – after a lot of trial and error. So much so that I had to use the simulator because I was building so much to get it working.