Any ideas how to solve this problem? Change the name, but not the skin, via plugin in 1.7.2 or 1.7.10
1.7.2 Player name change without skin change | Bukkit Forums

165416614s ago, by Antonio

+Antonio Noack Ahhh... Yeah after 1.6 they changed the packets

165386453s ago, by LostKey

+Lost Key I will try to spawn a new player and make him(the old one) invisible... but this would change the skin, too.... so there is no way it seems (because MC takes the skin directly from the name above your head...)

Just use disguiseCraft