UPDATE (11 PM, 28/02/2012): Digital UK information indicates that viewers receiving Freeview in the Channel Islands can retune after midday on the 29th if receiving from Alderney and St Helier relays and from late afternoon if receiving from St Brelades when the neccessary changes should have been completed. All engineering work should be complete by 5pm.
Two separate events are taking place on that day.
Firstly, viewers receiving from the St Helier, Alderney and St Brelades relay transmitters will need to rescan due to frequency changes, as the upper part of the UHF frequency band is being freed up for next generation 4G mobile broadband in both the Channel Islands, the UK and France along with the rest of Europe. The three relays affected currently broadcast on the affected part of the frequency band.
Secondly, following ITV Plc's recent acquisition of Channel Television, ITV2 and ITV3 are to be added to the Freeview line up, according to BBC News. This will affect all viewers via all transmitters in the Channel Islands. ITV2 will appear on channel 6 and ITV3 on channel 10.
The move to add ITV3 to Freeview in the Channel Islands will come at the expense of a timeshift version of ITV Channel Islands. The slot being used for ITV3 is used elsewhere over in the UK for ITV1+1 (or STV+1/UTV+1 in Scotland and Northern Ireland).