De-leveling question

[Bladeslayer]

im a 46 necro, want to hit lvl 50 and learn CDL and go back down to 46. so i can farm both aden dungeon, how far can you de-level before you lose skills you've learned? because the spellbook and SP is too much to have to buy again. Thx!

I was thinking the GM said 4 lvl's so it would be ok to do this. But cant find where he posted it