That's why I have
“make sure to justify deviations from” in there.
It's easy enough to make that policy, but you run the risk of making the development process too unwieldy to implement (See: Taligent's Style Guide).
I would hope that most style guides have caveats for deviation (disclaimer: I haven't read a style guide in eons, so I don't know what they generally say, these days).
I'd say that "We should do it this way, but, if you think your way is better, convince me." is a good approach.
Really, I see a lot of problems, caused by corporations' obsession with hiring lots of bad programmers, and trying to force them to be good programmers, by setting up strict boundaries, as opposed to just hiring a few good programmers, in the first place (which, admittedly, has its own issues). This is nothing new. I have seen this since the 1980s.
The really cool thing about software, is its flexibility. I feel that the enormous toolbox at my disposal, along with my experience in using said tools, makes it possible for me to develop some pretty good stuff. If someone tried to force me to do a "lowest common denominator" approach, I don't think the results would be good.