Add to documentation: once you create a case, don't modify your sandbox

A seemingly unintuitive aspect of cime cases is that, once you have created a case from a particular directory, it is very important not to change the code checked out in that directory until you are completely done with your case. Is that documented somewhere? From a quick look, I don't see this mentioned. Should this be called out as a warning in sections 1 and/or 2 of the Case Control System documentation in the cime user's guide?