I'm talking about dumping the subsequent bootloaders such as GRUB to a file located in a Windows-accessible location, and then adding a menu entry for Windows B

I'm talking about dumping the subsequent bootloaders such as GRUB to a file located in a Windows-accessible location, and then adding a menu entry for Windows Boot Manager to chainload into it. As far as I know, Windows doesn't just overwrite the BCD like that unless you explicitly tell it to. Also, obviously the assumption is Windows isn't a showstopper such as in my case. I'm inquiring if there are any practical or technical concerns that would preclude using WBM as a shim.