I've been lucky with my Mini Nova, it seems the bottom threads for the tank/head are either reverse-threaded or just very stiff since I haven't changed heads yet, and I can safely unscrew by the tank itself, though I do try and hold it by the bottom ring regardless. Little tough on my Vamo cause it sits flush but I figure the answer to your question, for me at least, is no times. I hate having to clean up a mess like high-VG nicotine-laced liquid all over my keyboard..done it once from spilling a bottle and don't plan to do it again.
Honestly, why don't tank makers reverse-thread the head connector anyhow to prevent mishaps like this? Would cost maybe another two cents per tank for the 'left-handed' threader and such..