I am on UK's worst network for updates - EE. Since 1320 CV version has Cyan rolled out, I didn't want to wait till Christmas to get this.
I've unbranded my 1320 with 3 simple steps found here -
[Tutorial] Unbrand (flash) Nokia Windows Pho… | Windows Phone 8 | XDA Forum
If you are in the UK, you need a EU CV ROM. Product is RM_994 and product code is 059V762.
If you are already on DP8.1 and are going to downgrade to WP8.0 anyway, I suggest downgrading to that ROM and firmware, which is unlocked, carrier free for European users. Then looking for update. It updates 3 times in total and you will be on Cyan! By end of this week if all the rumours are true, you should also have UK Cortana on it! ;)