Lexy,
By adjusting a resources capacity/Unit(%) the threshold at which they become 'overloaded' is also adjusted (up/down). Capacity for a resource can be set on the User Profile under calendar>schedule settings; at the task level in the resource info card to the right of the Work Plan in the Current Project view or in the Work Items module also to the right. Please join us for one of our open forum Q&A sessions to see a demo of this functionality.
-ps