The stupid thing about this is that regardless of which seat you select at OLCI they will try and charge you. Change from 22C to 22D and they’ll try and charge you. Once you have selected a seat and they try and charge you, you can no longer issue a BP for your flight until you pay, even if you reselect the seat they originally assigned you.
As previously stated, select the seat you want, break off the check-in without paying and at T-3 you can print your BP without paying. The process totally lacks common sense. Or, if there is a logic to it, I fail to understand it.