At the moment BBC One HD / BBC HD is not regionalised so I cannot watch my local programs I.E. NorthWest Tonight etal. when tuned into a HD channel. All I get is some muzac and a ident telling me to switch to BBC One (SD). So for me that's a deal breaker.
I'm pretty sure you can't do it. The stations are allocated to station numbers by a property in the broadcast called the LCN (which I assume means Logical Channel Number). When you tune the box either automatically or manually, when the channel data stream gets scanned for stations within, the LCNs are picked up and that's where the stations get stored whether you like it or not.