DISCUSSIONS on “Rules for online games in HoMM3 and formulas for calculating player rating.”

Max, if all skills are at their initial level, you won't be able to first max out Necromancy and then all the other skills immediately if you choose Pandora and gain 20k experience. Moreover, if all skills except Necromancy are at the expert level, but one slot is still empty, you still won't be able to do it – to max out Necromancy as the last skill, you need more than 20k experience. Therefore, this cheat won't work.