[Foreigner]

c4uran, Да можно просто перенаправить поток ошибок в nul (2>nul):

Код:

@echo off
setlocal

set "wmic=wmic PRODUCT where Name="McAfee Agent" GET IdentifyingNumber /value"

for /f "tokens=*" %%i in ('"2>nul %wmic%"') do 1>nul set "%%i"

if defined IdentifyingNumber echo %IdentifyingNumber%