Looking at apns, my suggestion would be to make that a synonym for the more descriptive apple-push-notifications. If there's a possible alternate use for apn, given the lower number of questions there, I'd just retag things. Also, you could leave a note in the tag wiki summary for [apn] directing people to use [apple-push-notifications] if they are referring to Apple's technology.
For example, there's the automatic-ref-counting tag, an Apple technology that many abbreviate to ARC, but arc can mean other things. Therefore, I edited the [arc] tag wiki summary to note that it was not to be used for automatic reference counting questions, and pointed people to [automatic-ref-counting]. That has significantly reduced the use of the [arc] tag, and I just retag the remaining questions that slip through. That seems to work reasonably well.
Unfortunately, I don't have enough upvotes in the [apple-push-notifications] tag to even suggest [apns] as a synonym, and getting others to vote on it might be tricky. This could be a job for the moderators.