Ive printed a bunch of harley davidson stuff. Trust me, you aren't going to get sued by Harley for a one off decal.
Given the laws here stateside, there is every reason for them to go after just about anything that could be conceived as against their property. Real or imagined. Now granted, the higher profile that it gets (in this day and age of "viral videos" that doesn't take much) that definitely increases the chance.
Companies like HD, Disney, JD I also think have in house counsel for this type of stuff as well. JD is one around this area is quite popular. What really throws a spanner in this, is that even dealerships, ones that one would think would have permission to go to anyone to get this done, may actually not. Usually there are deals with corporate with vendors and corporate is the one that still owns the branding, not the dealerships. And this goes with any national/international chain of whatever as well. Sometimes there will actually be an alternate logo that one could use for shall we say "unique" vendors that are able to get permission to do the work but not the usual contract vendor.
Now again, everyone has their own "threat" assessment and to each their own.
Then he sends me Harley Davidson logos and I said I will NOT print them because of the copyright. He went online and looked up the copyright laws and if we change this and that then it's legal and all these companies online do it so what's my problem.
If I'm not mistaken, the standard is really "how likely is one to be confused". If someone still thinks that it's the official branding, that can be no bueno. I'm unaware of an actual % of change law (although technically a 100% change is a % of change, so there is that).
I'm a non lawyer, so take all that for what it's worth.