Diskpart - hide or unhide a partition in windows

Type in a cmd : diskpart

To hide a partition type :

list volume
select volume 2
remove letter d

To make it appear back : 

select volume 2
assign letter d

If you mount the ESP partition like this, in windwos 10 you get an error message that you are not allowed to access it.
Open Task manager -> Run new task -> Browse.
Here you can access, edit, create, delete files. 

Or open Disk Management : diskmgmt.msc
 Right click on a partition and select - Change Drive Letter and Paths...
and then add or remove a letter.