Shaving off foam from seat back?

[70garyb]

So a bit off topic.. my top case has a backrest (Givi) which protrudes out too far and my girlfriend is pushed too forward. I’ve since removed the cushion and wonder if anyone has experience with shaving down the foam? I don’t know if the Givi cover is molded to the foam and thinking I’d need to buy new fabric but I’m more curious to know if anyone has shaved down seat foam that I could leverage before I make a mess of it. Bottom line I want to remove 75% of the foam high points and be left with a flat back.

Thanks