Paint touch-up can always be removed W/O damage to the porcelain. IT'S YOUR Sign, DO AS YOU PLEASE. Some of these guys that say NO, will place Clock Kits in pumps that had VR's & that is OK for them. HELL, I've made Twins out of Parts. IT'S What I Wanted.
I see nothing wrong with touching up any sign. Matt and Dick are right. It will always improve the look and it is totally reversible. No harm, no worries!
KJV Psalms 16:11
Thou wilt shew me the path of life: in thy presence is fulness of joy; at thy right hand there are pleasures for evermore.
I think we should be capable of enjoying the sign enough as it is. All im saying is the history is in the damage. To each his own though. But clean the touch up off before you sell it to me. Lol