While you're correct about the tag itself, that whole "in general" statement isn't really valid at all.
The only things that can cause the game to crash are duplicate objects (and even then, only when something crazy happens because of), and deleted objects.
Almost all of the entity tags have an effect during worldgen, and as such are immediately locked in. This is due to the way civilizations are set up, as I've attempted to detail in the spoiler.
Those two do not under any circumstances, and are fine to change with an existing world.
It's not that by having a world-gen effect tokens become "locked in", but rather that they will only perform/change their post world gen functions if they are added in later. For example if you add [WEAPON:ITEM_WEAPON_SCIMITAR:FORCED] to the dwarven entity after regen then it will perform only the "post world gen" functions, namely allowing your fortress to make scimitars, while not performing the "world gen" functions, such as allowing traders to bring scimitars.
As such the only entity tokens that actually "require" (meaning 100% of the time, sorry if my wording was confusing) a regen are the ones with
only world gen effects. It's just that to have the "full effects" of many you
will need to regenerate.
Really the best way to sum up most entity tags is similar to your description of biomes as they "are highly relevant during worldgen and may not entirely have the desired effect" but they still may have
some effect, namely the ones that dictate what you can make and what weapons/armor are considered "foreign" in your current fortress.