So I was thinking about how we could get sponsors on helmets and I came up with following idea:
So basically Codemasters reworks every single helmet design and adds a "Sponsor layer" on top of it that looks like the real ones design wise (e.g. Monster Energy stripe for Mercedes) and suits the helmet design as well. Now if you join Mercedes the game will add the "Mercedes Sponsor" layer onto the helmet. If you decide to leave them for Ferrari the game automatically removes that layer and adds the "Ferrari Sponsor" layer to the helmet. Now if you drive the multiplayer or classic cars it simply removes the layer entirely and the helmets look like they do in F1 2019, so completely sponsorless.
That way you only have the official team sponsors on your helmet and you can´t mix anything up (e.g. Red Bull logos on the helmet while driving at Williams) and it would kind of work like the race suits and caps in career mode that also lack any bit of personal details like name, number or personal sponsors. I belive that should be a possible solution that the sponsors might agree on if codemasters is ready to put the effort into it and rework the helmets.