Changes your gunsight settings...
As in your reassignment of the historic default setup gunsight menu to different planes or, your own custom gunsights being replaced with the default historic gunsights?
If this is what's happening, before you run a new patch, backup a copy of your current sights folder. After the patch if your gunsight settings have been rearranged, copy the backup folder contents into the new sights folder. At the least, all files with a .txt from the backup to the patch updated sights folder. The .txt files hold the gunsight setup info for each aircraft.