I like the fiberglass brush idea.  I already use one of those for cleaning off the 'blackening' on weathered rail.  I'll try the paper towel with Solvaset trick also.

In most cases the renumbering is the same number of digits and identical lettering size as what's there now, so the new lettering and some light weathering makes the new decal numbering sort of disappear.  I've done some with scraping and sanding, and it's not too bad but not that great either.

All for building ten or more Branchline cars from a given series where four numbers were produced in the original run.  I should note that this occurs, for me, on Stewart three-bay offset-side hoppers also, but for the hoppers, since the cars are black, I have no trouble matching the paint with a little masking.

Ron Merrick