For non-TTIGs, TTN needs some additional information such as frequency plan, at least if downlinks are needed. (Maybe it accepts uplinks no matter what?) But today, the TTIG is a bit special in the V2 backend, it being auto-assigned the frequency plan:
Q. Is registration in TTN Console required?
Yes the registration is mandatory. For now, these gateways are identified as US915/EU868 based on their EUIs and a default frequency plan is sent out. But, with the official V3 support, you can select other supported frequency plans while you register your gateways as you would do with other gateways currently.
That’s all I know. 
While true, it seems one can transfer ownership from its settings page.