I am now in the following situation for the third time:
I have detected a need for a new tag and I am sure about this (e.g., as I have successfully proposed this on the respective site meta) and there already is a fair amount of questions to which this tag should be applied.
What is the best practice as to mass-applying this tag to old questions? My main concern is that doing all of this at once may be a severe disruption on sites with lower activity, as all of these questions get bumped.
While a similar question has been asked before, this was some time ago and applied to Stack Overflow, whose activity is not on a totally different scale than the sites I am worrying about.