Yes, it is theoretically possible to do a hardware downgrade to 5.05. : r/ps4homebrew
iFenix on Twitter: "Playstation 4 | 7.55 down to 6.72 | Downgrade!!🔥💪 Another FW Revert success! By - @Centrinouk SYSGLITCH_DOWNGRADE : https://t.co/HpLjtfHssH https://t.co/Lj2QGacMPf" / Twitter
Downgrade PS4 Firmware From 7.55/7.05 to 6.72 and Below - YouTube
Can you downgrade your PS4 system software from 6.0 to 5.05? - Quora
How To Downgrade PS4 From 5.55 to 5.05? #GS2 - YouTube
Downgrade de PS4 5.50 -> 5.05? - Forocoches
How to update your PS4 to firmware 5.05 - Wololo.net