You do not need an electrical contractor license to change acrylic/polycarb faces of backlit
signs. You do need a license to perform any electrical task to a
sign, including changing the bulbs. Also, per the letter of the law, you need a license to conduct "business of designing, manufacturing, installing, connecting, reconnecting, or servicing an electric
sign, cold cathode, neon gas tubing, or outline gas tubing, or altering electric
sign wiring or conductors either inside or outside of a building."
As far as getting permits, the permitting office is suppose to deny applications unless there's an electrical contractor attached (meaning you have to have a master electrician as a w2 employee). But, the TDLR is the one that needs to notified of it for you to get in trouble. We had another
sign company wait until we lost our electrician before they called the TDLR on us for installing (and advertising on our website) electrical
signs. We got a new electrician shortly after the "friendly" letter from the TDLR, so all was fine with the world.