Folder:
db/pre-re (or re)/
mob_db.txt
Poring:
1002,PORING,Poring,Poring,1,60,1,36,20,1,8,1,2,5,6,1,1,0,6,5,10,12,1,3,21,0x83,400,1872,672,480,0,0,0,0,0,0,0,909,7000,1202,100,938,400,512,1000,713,1500,512,150,619,20,0,0,0,0,4001,1
Example:
909 = Jellopy
Change it to 607 (yggdrasil) and poring will drop ygg instead.
Just find the item ID and change to what you want.
@edit
Don't forget to use the command @reloadmobdb after edit.