I did and it still stayed locked.
Looking at screens.rpy, I see cg6 is referenced as: image cg6 = "images/cg/cg6.png"
In the images/cg folder, there is no cg6.png, it's "bonus doodle.png" (which is what's referenced in script.rpy)
I don't know the gallery unlock logic, so not sure if just changing the name would be sufficient or not. (I just know renaming bonus doodle to CG6 did NOT fix the gallery and just broke it in the main game (no surprise with that one)).
Edit: But what do I know... "cg2.png" doesn't exist either (CG2-2-2.png in the folder), but the karaoke CG shows up fine.
Edit 2: lolol at the commented out credits Afterword for Love Goes Toward Love.