Making custom grid fins adds a lot of parts and is time consuming, plus some don't even work like real fins! My idea is to have a procedural grid fin (kinda like wings) where you can shape it like a wing but if you shape say the left side of the grid fin it applies the change to the right side so you will always have symmetrical grid fins. The grid fins can have the same input as wings (None, auto, pitch, roll, etc, etc) and generate control to help guide the craft and, you can choose if you want them to have pointy edges or not!
Edit 1: You can choose to have them open on start or not but are stowed away by default and when you activate your set AG say AG 6 it will open and you can use it.
This is kinda like PasonJawulo's request with the landing legs

this may be asking for to much ;-;

(to the devs if they see this: if adding pointy things to the grid fins is too hard you can leave them out)