I've just applied for the Notice of Variation to allow me to change my callsign during the period of the Queen's Diamond Jubilee where it will become GQ4VXE and then during the Olympics when it will become GO4VXE
Should be fun!
The process is simple. As long as you have your OFCOM Lifetime Licence Number! I didn't and had to scrabble around on the OFCOM site to get that. Once I had it, I had the online forms filled in and the NOVs in the form of PDF documents emailled back to me immediately.
You can apply here