from a strict reading of the new T&C that means

once you complete ONLINE check in - you have no chance of changing, even at the airport?

people who are affected
1. those who redeem on another program (e.g. status-less BA) which doesn't allow you to change FFP number easily

2. Another group that i see affected are those who are changing FFP programs - e.g. BA to MH. i am lucky that i have now managed to switch from BA to MH Emerald - i.e. for a while this year i had to rely on my BA status to go into the lounge, whilst crediting to MH to build up new status...