After upgrading to Windows 10, I realized that I could no longer access the mounted EFI partition even when explorer is running with admin privileges!!
It took me some time to find a workaround so I thought I share it.
1- Mount the EFI partition to a free mount point:
-- Run command prompt as administrator
-- Type "mountvol X: /s" (without the quotes, X being an unused mount point)
2- Use Explorer++ (Free, Open Source app) to manipulate the files on the partition:
-- Run Explorer++ with administrative privileges
Hope you find this useful