I think the game could really use a UI feature like this. It's less functional, than adding customizable building subgroups, but that was a feature, that would be pretty intrusive on the UI and many players wouldn't really on a glance know what it is meant for. This strikes a nice balance.
If I can add my input a bit - I'd like it so the icon for a PM doesn't show "mixed PM" if all of them are set to the same one, except the ones that are locked. It should have a different icon, which shows the PM and maybe a little thing next to it, that indicates "not literally every single one".
And it would be nice if there was a way to bulk apply PM only to incorporated states. It's a bit weird you gotta apply stuff to African Colonies and Trade Ports when trying to change mainland PMs.