[Stooky Bill]

DVB-S2 is the modulation standard for HD, although DVB-S can he used for HD I don't think it's the done thing.

I doubt they'd need to negotiate with Astra, as long as the uplink is on the right frequency, not putting out too much power and conforms to their technical standards they don't care what is done with it. For the changes to happen they'd need to know as the uplink needs to be cut and brought back up

They may need to bother SES because on Astra2 DVB-S2 tranponders tend to be wider with a symbolrate of 23000 instead of 22000.

Yes, they'll need to know the parameters of the uplink, but as long as the new symbol rate isn't one that takes the uplink out of the bounds of the transponder then they won't have an issue. Changing the roll-off has an effect too, making that smaller makes the carrier effectively wider.

Most of the transponders have a symbol rate of 27.5 so either the BBC have ones that have a smaller bandwidth or they're conservative with them. EIther way 1 extra M/Sym won't make a difference - their DVB-S2 transponders already use that

But then again if Jimbo is right they will switch and the data in the EPG just reflects what the transponders are looking like now and not how they will look.

I'm not sure what you mean. The change to the transponders and the change of the EPG are two seperate processes and impossible to do instantaneously.  

The transponder will have to go off air to make the changes... you can't just change things like symbol rate and modulation type on the fly. Plus the data rate of the new line up has to be correct before going to air with it. 

I'm not how EPG changes work - when they're done (overnight or during the day) and how long they take to react on people's boxes at home - whether a viewer tuned to a service loses it when it is being pointed elsewhere for example. But co-ordinating the two will be tricky, they will want to have the new transmissions up and running for a bit before making the EPG changes, especially where the existing HD service is moving

My guess is that all the SD LCNs on a transponder will be pointed away to the nightlight, then the transponder will close and the changes made. Once that's been on air for a few days the EPG changes will be made to point HD LCNs to that transponder.