No problem. I know you as a member well enough to know there was no offense intended or implied.Good point - sorry about that!
That's fair enough. I don't think that variant rule specifies that it is an action to use a spell but I would guess so.Not exactly the same thing. There are several monsters with variants in the MM, but they are built-in rules. And I would argue that, IMO, by default the rules are there to use if you want.
Note you said they "don't have them." This, to me, would give the impression that you would need some sort of houserule to give them spells. But you don't, the rules are right there for you to use. IMO, it is more akin to giving an Orc a sword instead of a greataxe. You are just picking the spells (like picking a different weapon). Except even more "default" as it mentions in the monster entry that you can do this (instead of the introduction).