[sunnykey]

Код:

@echo off
setlocal EnableExtensions EnableDelayedExtension
chcp 65001
set cfg=%tmp%\dp.cfg
set log=%tmp%\dp.log
echo Get volume list
echo list volume > %cfg%
diskpart /s %cfg% > %log%
echo Get USB drive letter
for /f "tokens=2-3 delims= " %%i in ('findstr /c:Removable %log%') do (
	set num=%%i
	set ltr=%%j
)
echo Change USB drive letter
echo select volume %num% > %cfg%
echo remove letter=%ltr%>>%cfg%
echo assign letter=X>>%cfg%
diskpart /s %cfg%
echo Remove setting
chcp 866
if exist %cfg% (del %cfg%)
if exist %log% (del %log%)

меняет диск на горячую
З.Ы. Тестировалось с одной флешкой