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.
BBC1 is on LCN 1, BBC1 HD is on LCN 50.
If you pick up signals from two regions so there are two different channels on the same LCN (BBC1 West and BBC1 Wales for example), you get asked which region you want and the other one gets bumped into the 800's on a first come first served basis.
Your only other option is to allocate Favourites.