What is Firmware.scap in the /EFI partition? I'm looking at the /EFI partition, and it has 2 .scap file.

/EFI/APPLE/FIRMWARE/MBP112_0138_B18_LOCKED.scap

and

/EFI/APPLE/EXTENSIONS/Firmware.scap

They both have 2 files with GUID's that are present in the other, however the contents of each are different.

The file with the GUID C3E36D09-8294-4B97-A857-D5288FE33E28 in /EFI/APPLE/FIRMWARE/MBP112_0138_B18_LOCKED.scap contains the text $IBIOS$  MBP112 88Z 0138 B18 1610201654 Copyright (c) 2005-2016 Apple Inc. All rights reserved.

However the file with the GUID C3E36D09-8294-4B97-A857-D5288FE33E28 in /EFI/APPLE/EXTENSIONS/Firmware.scap contains the text N $IBIOS$ ROMEXT1 88Z 0002 B00 0710231738

What is the Firmware.scap file, and how come when I delete it, nothing changes except that it boots faster?
I suspect the second file is a security update. The 1st one most certainly is a no-fly zone.
Has to do with firmware I think.

However, never ever mess with your (U)EFI partition, or you may have a very expensive Apple doorstop on your hands...

Well, my own EFI partition is mounted here. You can mess around with it all you like on an external bootable USB stick.

I'm doing this just to see if I'm able to run an unallowed version of OSX on a very old, already scrapped Mac Mini.

OS bootloader seems to depend on (U)EFI, namely...
Revive a broken bootloader/ EFI partition, and you may do wonders. I think.

Just look at this:
http://xpcboot.weebly.com

Have fun, but don't break a working Mac...