Take a look at Red Eagle LXIX's work: https://7daystodie.com/forums/showthread.php?94219-Red-Eagle-LXIX-s-A17-Modlet-Collection-(UI-Blocks-Quests)
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I'm sorry, I'm not clear on what you are looking for.
Is this the new code you want to add?
<passive_effect name="PlayerExpGain" operation="perc_add" value="0.15,1.35" level="1,9" tag="zombie,walker,feral,radiated,hostile,animal"/>
<passive_effect name="PlayerExpGain" operation="perc_add" value="1.5" level="10"tag="zombie,walker,feral,radiated,hostile,animal"/>
If so, which file and location did you want to add it?