Boot Protocol

[KARL]

For ease of flexibility/movability I use a bootable hard drive with all my essential stuff on it and simply take it anywhere I go when appropriate. I had a replacement created but without prior consultation with me the new one was not set up with Legacy boot (i.e. everything the same) but instead UEFI was installed. The new drive (UEFI), which so far has only the operating system and applications on it (Ubuntu - no data files), cannot be used everywhere I have so far taken it (equipment tried) whereas the old one (Legacy) can. I want to change the new one to Legacy, but how complicated is that change ? Can the relevant sector (UEFI) simply be surgically altered/replaced to/with Legacy or is it a case of starting right from scratch wiping the drive clean and reinstalling not just the boot sector but also the entire operating system and the applications ?

[ToraToraTora]

I'd say you'll need to copy your files off and reformat completely. Some ideas here though:
https://appuals.com/convert-uefi-to-legacy-bios-on-windows-7-8-and-10/