Modding the XP is useless,I tried it already and all it does is showing the modded value.
For example I had a save with 1520 XP,I modded it to 3995 cause I need 4000 to level up.
When I loaded that save it showed 3995/4000 xp,When I gathered 50 XP for killing a enemy I got the notification for getting a skillpoint to use,but it was still at 2 as before.
It also counted past the 4000 XP needed,it showed 4045.
Meaning it is useless to mod the XP,unless you can find a way to also input the value needed to next level(So it will give a skillpoint when reaching the XP needed,instead of counting on and pretending to give a skillpoint)