@OP,
You can preserve your pilot careers by copying the following folder to somewhere else, and then re-copying back after a new WoFF installation (or re-installation):
OBDSoftware/WOFF/OBDWW1 Over Flanders Fields/campaigns/CampaignData/Pilots
If you prefer a more automated approach, recommended is to look for RJW's "Pilots Backup Utility" that is available on Sandbagger's mods. website for WoFF.
Cheers & good pilot backups to you,