Is it possible to change GL product group yourself?

Ever since I started listing with EANs I’ve had the nightmare of what seems like each product being assigned to the wrong gl group. I set its category at creation, but then its gl group in the back end is assigned improperly. My products are automotive parts which I add Part Finder fitment information to, when the wrong gl group is assigned I am not able to add Part Finder fitment information.

The products should be assigned as “gl_automotive” but they are being set to “gl_biss”.

I’ve previously told Seller Support the issue, and it was actually a support representative that told me in the first place that it was because of the GL groups that I cant add fitment information - that support person was actually pretty helpful as they fixed the issue for me.

However, now I’ve got the issue affecting other new products, I’ve told Seller Support what the exact issue is and even referred them to the other case where it was solved.
But in usual fashion, Seller Support is woefully incompetent. They’ve come back to me twice telling me the issue is resolved, but it never is. Now I’ve been waiting a few days for another response, which I am guessing will be to tell me a third time that it’s fixed when it’s really not.

It’s taking too long now and I would like to know if I can fix this myself. I’m pretty sure the GL group is changable by CSV, but I worry that changing it could cause an issue with my listings. Has anyone done this or can offer some advice in how I can best get this fixed.

Cheers