Firmware update and going backwards

[Guest Andrew Montreal]

Hi all,

 

I am doing tests with my new video card. I created a new drive for all this to keep me original drive intact. It requires that I move to high sierra. I am presently at El Capitan. It also requires that I do firmware updates, both for High Sierra as well as Mojave. If I do these firmware updates will it prevent me from being able to return back to El Capitan with my original hard drive?

 

Thanks.

 

Andrew

 

Source: MacRumors