While it appears like an easy task, I believe it isn't as much. The currently used gas-laws is not specifically about ideal gases, as the excerpt clearly states:
Physical and chemical laws describing the properties and behavior of gases.
Yes, the tag is broad, but in my opinion not too broad. I personally don't find it necessary to separate real gases from ideal gases. There is a significant portion of questions that deal with both, those would also have to bear both tags.
I am unsure whether this has enough merit to go through the following:
It is one of our top tags with more than 400 zero or higher scoring questions. This makes any change in the behaviour of this tag much, much more difficult. We would have to screen each and every question, as orthocresol already pointed out in the comments, if the renamed tag still applies.
As a minor concern, we introduce another possibility for misapplying tags. I don't think that is much of a problem, given that almost every question will be edited at one point.
From that point of view, I am strictly against modifying (renaming) that tag. (Anecdote: The homework tag's excerpt states: Do not use in all caps, but it is applied at least a few times every week.)
Instead the better way to do that would be to phase out gas-laws by introducing ideal-gas and real-gas and systematically replace the former with one (or both) of the other. That way you have at least some control what has been done and what is still to do.
That obviously means that we would have to go through 400+ questions, and given the experience with reaction (boo!) and homework (see Spring Cleaning Chat) it seemingly almost takes forever to go through just a handful of them. Obviously cleaning up the tags involves cleaning up these questions to the best of your ability, including any answers.
Unfortunately, there are currently not that many people working on these minor issues. I would like to point out, that there are similar (more complex) projects still being dealt with, like the functional group/ class of reactions reorganising. There is plenty of homework to keep us busy for the next years, and there is still some reaction left. Personally I'd rather focus on ridding us of these remnants other than introducing another retagging project, especially since another TRE seems unlikely.
In summary: While I am not against doing this, I'd put it on the "'t'd would be nice" pile of things. The current tag system is not broken and doesn't require immediate action, so better wait a little longer.
Postscriptum; I am always looking for people helping out with some of the earlier mentioned issues. For this purpose the spring-cleaning chat has been continued, serving as an catch'em all documentation service. Occasionally we decide about the fate of some questions. It's open to everyone, and it would take some work of orthocresol's and my hands (and for a long time Brian's, too), which would be very nice, if you drop in and help out a little.