well killing can still net u XP but it shouldn't be tied to the quest which is stealing the crown jewels. but i like what handefood's suggesting & what alrik is wondering: alternative to killing which is sneaking past the guards/whoever.
in lionheart, XP is awarded to sneaking up to 75% of the total XP that u get if u kill. so since u don't have to face the hardship of actual killing & risking your neck at the same time, 75% is fair enough. for me at least.