It used to be allowed, but in the current (collectors edition/living) rules, it is not.
The current rules allow Player Assassination during a Topple by play of a Black card in hand at the cost of 3 gold plus 3 gold for each troop in the victim's Private Army.
The older rules (at least the copy I have) allowed Player Assassination by play of a Black card in hand at the cost of 10 gold - but was not allowed if the victim had a Private Army.
As I read the older rules, this was allowed only during normal play of Black card as an Action - and not during Topples.
Is that correct?
Was any gold stolen? (I suppose that I should ask that about the current rules also.)
Was the cost in Actions dependent on the current Regime and what was printed on the Black card? (That is not the case now, since Player Assassination does not require an Action now.)