Idolator lord mark change

Idolator lord let's you change your Undivided cultists to a choas god that the lord has.

Am I right to say that having the khorne tag is different from having a "mark of khorne"?

Like if I gave my cultists khrone Will they have the 1+ attack on charge or would nothing change?

And If they don't gain the mark abilities then what is the use of having a chaos god tag?