So did I. I did the conversion before there were any directions.
Since format is a write operation, formatting a drive in the parity array updates parity so parity will continue to be in sync after the format. This actually trips up some people (despite warnings in the webUI) who hope they can rebuild a formatted disk to recover its data, but parity agrees the disk has been formatted.
Steps 5,6,7 in the wiki cover how to actually do the format.