I would like to share with community one information witch may be obsolete as I am not an active user here. If that is the case please remove that post.
According to all official information Windows 7 may be installed on NVMe SSDs only in UEFI mode.
According to my knowledge this means GPT partition only (UEFI does not allow MBR partition AFAIK).
This site informs about "ThinkPad BIOS updates that allow for legacy booting to NVMe SSD. With the BIOS update, Win7 can be installed to a MBR partition, even on a NVMe SSD. So if you don’t want to modify your Win7 image to use GPT parition and UEFI boot, then you can update to one of the BIOS versions listed:
ThinkPad T460s: version 1.11 or newer
ThinkPad Yoga 260: version 1.41 or newer
ThinkPad X1 Carbon (4th gen) and X1 Yoga: version 1.14 or newer
ThinkPad P70: version 2.03 or newer
ThinkPad P50: version 1.24 or newer
ThinkPad T560 and P50s: version 1.06 or newer
ThinkPad T460p: version 2.04 or newer
ThinkPad T460: version 1.10 or newer
ThinkPad X260: version 1.19 or newer"
Maybe someone will find that information useful and after extracting proper module(s) from ThinkPad BIOS will allow “mod” other BIOSes to similar functionality. 
This may give alternative way to mod BIOSes to allow use NVMe SSDs, and maybe will allow to mod also some very old motherboards to function with NVMe SSDs.
EDIT by Fernando: Thread moved into the better matching Sub-Forum and thread title customized
Actually UEFI does allow MBR table. But you may get a BSOD if you have different partition tables of disk drives (e.g. an SSD with GPT and an HDD with MBR table) connected when booting Win7 or 8.
Furthermore, if your UEFI BIOS contains an NTFS DXE driver(you can manually add the DXE driver into it if it doesn’t), you’re able to switch to UEFI boot mode painlessly by just adding EFI boot files into C: partition
bcdboot C:\windows /s C: /f UEFI
@trodiac:
Since your method to get Win7 installed onto an NVMe SSD in LEGACY mode doesn’t require any BIOS modding, I have moved this thread into the better matching Sub-Forum “NVMe Support without BIOS Modding”.
Furthermore I have shortened your thread title.
I hope, that both changes are ok for you.
That really isn’t that usefull… here’s a set of problems :
1) There are no NVMe drivers for anything older than Win 7 x64/x86
So you can boot, but you can’t initiate older OS (which is the main point of Legacy mode in the first place).
2a) Pretty sure all laptops on the list have UEFI BIOS already, so… why would they need NVMe drive in Legacy mode ?
2b) How do you put a NvmExpressDxE module, into a non-UEFI BIOS ?