I'm also interested in this process, but in my case it would be removing modern factory applied lettering on a couple of steam engines and tenders..
Correct me if I am wrong, but I think most manufacturers use some fairly sophisticated processes for lettering now rather than decals--possibly some form of computer controlled laser printing application that is a lot more sophisticated and precise than anything available to the hobbyist.
I do know that there are a variety of erasers available at art supply stores that have fairly low abrasive qualities so as not to damage high quality art and drafting papers when making corrections..
Cheers