To make changes to BCD stores OTHER than the Boot store, use the /store switch. For example, this command:
BCDEdit.exe /set {default} TESTSIGNING ON
becomes this, instead:
BCDEdit.exe /store D:\Boot\BCD /set {default} TESTSIGNING ON
this is, of course, assuming one hard drive, the hidden boot partition, and booted from standard WinPE, causing the hidden BOOT partition to be assigned drive letter D:
ZC