Is it possible to reroll either a magic or rare necro wand to get

+5/6 Skellies & +5/6 mastery?

If so, how?

Cube:

Magic item +3 pgems
Rare item +6 perf skulls

If i remember right

magic can have +3 summoning
magic and rare can have +2 necro or +2 summoning
coupled with staff mods, 5-6 to skills are possible

however, rerolling anything but charms is usually a waste of time, since there is a huge number of possible affix combinations

Yeah guys but it's not that easy, those staff mods are low lvl and +2 skills or +3 summoning requieres certain ilvl. That's why im asking on a topic.

+2 +3 skills available at "mid" i lvl no? Lvl 70 should be enough to have the chance for those affixes, but i bet there some calculstors for that somewhere.

Maybe theres a "best" lvl to reroll those, like min anf max lvl to cut out the possibilitys for high req affixes you dont want

Yes.

A rare polished wand, ghost wand, lich wand, or unearthed wand

rerolled with 6x perfects skulls on a level 1 character over and over again will eventually reduce the ilvl to a low enough number to acquire +3 skeletons and +3 summoning skills/+2 necromancer skillls.