BITS Compact Server, can this be installed on Windows 10 Pro

Turning RAID off seems like a Bad Idea™, but you're pretty well suck unless you can plug a USB drive into the server or something like that. You can shutdown the machine, cancel the merge, the grab the vhd and avhd files. Once you move them Hyper-V will no longer merge them automatically, you'll have to do it manually. Once it's merged move the vhd back to the original location and Hyper-V will automatically pickup that the avhd file is gone.

using a shared login account, this isn't possible. part of BITS is the ability to restart interrupted file transfers, which it does by reading the end of the file to know where to restart at. so the ability to put a file will always require the ability to read the file.

an option might be to instead of using one account to login as, create a group of all of the machines that will be sending files. give the group modify access to the folder (but not the subfolders and files). also give CREATOR OWNER full access for files and subfolders. use the machine credentials to log in. with these permissions, only the machine that uploads a file will be able to read the file.