You don`t have 2 flash both main and FS, if you don`t want to lose your settings.

You can flash only FS and upload another customization.

So, if you have a R8BC004 fw, you flash only K770i_FS_EUROPE_5_RED52.fbn.
and HB1-06_Gen_CDA102568_14_R8A_GENERIC_EUROPE_5