Maybe. His appearance was brief and it was only an Easter egg that confirmed that it was actually him so it would be a very small retcon.

Mcu Johnny Blaze aka Ghost Rider and Ghost Riderverse Johnny Blaze Ghost Rider as well as both versions of Blackheart and Mephisto

Depends

Gabriel Luna would like to come back as Ghost Rider for the MCU so I really hope he can return

Now if Johnny Blaze appears not sure how this would work

Hope so. Any way to add Ghost Rider into the MCU is a great plus! Any character version (Blaze, Ketch, or Reyes).