Can I add an ability to a monster in the compendium

Lets say i want to make a Winged Kobold Shaman. Can I take the Winged Kobold from the compendium and add Spellcasting ability to it? I've tried dragging and dropping the ability and spells into the monster character sheet but nothing happens.

Yes, this is possible, in fact, I just answered this same question yesterday. :D I am assuming the D&D 5e by Roll20 sheet. Let me know if you are using something else. Put he NPC in edit mode (click the upper right gear icon). Near the bottom you will find a check box. Check to make sure the monster is set up to be a spell casting npc. For instance, if I drag a spell onto a lich, the spell is added. If I drag it onto a goblin, the spell is technically added, but won't display. So click the option to make it into a spell caster: Before: After: Dreaded Goblin-With-A-Magic-Missile:

That did it, thanks!