How to make a quest reward custom XP amount?

Hello, I was trying to make few custom quests which will reward a huge amount of XP (enough to instant level someone or near that) but I can’t find out how that works.

I am using the Truice program and I don’t see any option to reward a certain amount of XP. I notice there is RewardXPId and RewMoneyMaxLevel however I don’t fully understand how the system works.

I imagine RewardXPId takes the XP amount from some DB table or DBC but I couldn’t figure it out.

Another question, is it possible to make a quest remove XP from a player lowering his level? Perhaps set a negative value at XP reward?