Only thing you are going to be able to do is to "dig out" the laquer and peel/soak off the old decal, then re-decal and laquer. Quite a big job for what you will gain.
I had a similar problem when I bought an SPS seat unit, so I got my local graphics shop to do me some small vinyl stickers which simply said "NOT A" and stuck them in front of the decal. Not very elegant, but caused a few laughs. I don't take these things too seriously, few too many "Brand" engineers out there!
