My laptop is a Dell Latitude E5430 that supports both EFI and "legacy" boot modes. I'd like to removed win8 and it's troublesome EFI stuff and replace it with a Win7. I'd like to keep my ubuntu installation along the way, but it's okay if I have to reinstall it.
EFI by itself isn't troublesome. Windows 7 also supports (U)EFI very well, so you can easily wipe the Windows 8 partition during the Windows 7 setup.
EFI is the mode of the firmware itself. If you want to change back to legacy BIOS (oh boy, it really is legacy, possibly the oldest artifact in today's modern PCs), you have to also change your disk partitioning type from GPT to MBR (for windows). Considering that UEFI is definitely faster in booting than legacy BIOS, I'd suggest you take advantage of UEFI here.
You can retain your Ubuntu installation whether or not you're sticking with UEFI.
If you wish to go with UEFI, drop a comment and I'll edit this answer and point to what you need (not much) to install win 7 in UEFI.
But to answer your original question : Since you have no data to save, nothing is unsafe in your system, including switching out of EFI mode.
ADDENDUM: So Windows 7 supports UEFI well, but most setup discs that you might have burnt or even obtained from MS, don't support booting on UEFI. This is not so much telling on MS's inadequacy, as the sheer craziness of making a DVD bootable in 2 different ways. So you have 2 options :
- Format a USB flash drive in a particular way and copy all files + folders to it. This is not only fast, it's less complicated. This process is detailed here and here
- However, if you're like me, and want to keep one DVD around without having to format and copy to a UFD each time you want to reinstall, you've to do a couple of more steps. This process is detailed here , check Samuel Tai's Answers. You can tweak around with the command, but use -udfver102 only. Later versions are not boot-friendly (personal experience).
You can't remove UEFI (don't say "EFI", as that refers to an obsolete standard) from a laptop that has it installed in its firmware. You can't go back to a plain old BIOS. However, you can remove Windows 8 and the "(U)EFI System Partition" and boot from a disk/OS that only supports BIOS boot mode -- this will work because most/all UEFI firmwares support compatibility mode with BIOS boot method.