Please refer to your books and do not invent procedures. We are talking about aviation and not potatoes buisness.
Nothing will happen if the FAF becomes the FROM waypoint? How can you say that? Not 100% true, depending on the type of approach , Which automation you are using and from where you are being radar vectored.
Quick reminder FCB-FCB23 P 6/8
CAUTION : "Before arming NAV, check that the correct "TO" waypoint is displayed on the ND. ‐ The intercept path in HDG/TRK must not cause premature sequencing of the FAF. The FAF should be sequenced in NAV mode, when established on the final approach course."
Another reminder from FCOM GEN P 10/34
Definition of CAUTION: "An operating procedure, technique, etc. that may result in damage to equipment if not followed."
Another one that could help...
FCTM:NO-110 P 2/8 : "A good cue to monitor the proper F-PLN sequencing is the TO waypoint on the upper right side of the ND, which should remain meaningful. If under radar vectors and automatic waypoint sequencing does not occur, the F-PLN will be sequenced by either using the DIR TO RADIAL IN function or by deleting the FROM WPT on the F-PLN page until the next likely WPT to be over flown is displayed as the TO WPT on the ND."
I would like to add this one
FCOM PRO-NOR-SOP-19 P 15/20: "Check correct TO waypoint on the ND"
Obviously the aircraft will not fall from the sky just because you wrongly sequenced a waypoint. Also you could say that nothing will happen if you switch off the MCDU and nothing will happen if you activate approach phase in cruise and fly selected 0.78 . But why would you want to do things upside down? Instead of doing a documented procedure like a professional?