You are saying that you can scan and retain channels higher than 125, but just not able to rename it, right?
For MC 10, try editing this registry key:
HKEY_CURRENT_USER\Software\JRiver\Media Jukebox\Properties\TV Channels
(Start->Run..., and type regedit in Open: box, and click OK. Navigate to the key above).
The channels are saved in the key as string values, with names like "Channel ###". You can edit the names.