You could try using a Material Paramter Collection and simply reference it in your character’s blueprint and fire an event that uses it. Sorry for the lacking detail, I gotta leave, but figured this could get you started.
Edit: Got an extra minute, haha. Set up a Material Paramater Collection that has one Scalar Value, call it something like “EmissiveMultiplier” and in your texture, use that scalar and multiply it by your emissive texture and plug the result of the multiplication into the emissive value. This way, you can use “0” for off and “1” for on.