Well, you can determine what is displayed on the screen, Font and Color I believe, maybe size too. You get to pick a duration, which you can set to whatever works for you. It wouldn't be that hard (I don't think), to include a check box or drop-down option for the "banner" to be persistent until the mapped key (toggle or two-step) advances or toggles.

That way, if you want a persistent message/reminder, you can have one. And if you don't want it to be persistent, it will clear itself after however long you have set.

My Melee IWT mapped key, which is frequently spammed along with my click castsequences does IWT for only the melee group, and does not spam an IWT message. My single press, every toon gets it, IWT mapped key (different hotkey for the Mapped Key, but same output in Warcraft) announces in pink lettering that IWT has been pressed; it's pretty easy to set what is displayed and when.