1 - that's a GS system so you can't do that , just you can maybe to let for example people get gold/etc from roc mt mobs while they are lvl 110 or more , By change the mobs level at server side , But the players which are around the mobs lvl can't drop for them items/gold , But exp and HP for mobs are same so those players can attack at roc mountain without problems .
2 - By changing the mobs Cuz the drop system depends on mobs lvl
to do that , open RefObjCommon table find out the mob u need to change it's lvl , go to last column which named link , find out the link number and , Open RefObjChar table and find out in it the link number at ID column .
3 - you need to add them in server side too (database) there's many guides how to add items to NPC .
at Last don't forgot when u apply change for example to mobs lvl u need to do same at client
and also i was GM Tarky at this server (Titan) who's made the roc mountain system