Yes, but you need to be extremely careful.
1) Only turn the head on, but leave it on standby (ie. no sound if you had a cabinet attached)
2) NEVER EVER turn standby off!
3) Take the FX loop send signal from the head into your line in
4) Record it and apply an impulse to it
If you want to monitor it while playing, add an impulse VST with zero delay (KeFIR, for example) and load a sample into it.
the standby cut the high voltage, so if what you said really work, the standby don't do his job haha, you need high voltage on preamp tube