Beg to differ.
On an aluminum head you want the engine stone cold when pulling the plugs. Heat expands the metal, which makes a tighter fit. Pulling plugs on a stone cold aluminum head minimizes the chances of pulling the threads out.
If they are already siezed, I guess anything is worth a try as you'll end up having to helicoil the plug holes anyways. Use anti-seize and a torque wrench when installing spark plugs.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.