Can I give the managing agents who collects the levies, the instruction to add interest on any owners overdue accounts

I am the Vice Chairperson of my Body Corporate in JHB and also the Trustee responsible for finances. A clause in the contract that each resident signed with the developer states that interest will be levied on overdue levies.
 
Can I, as the Trustee responsible for finances, give the managing agents who collects the levies, the instruction to add interest on any owners overdue accounts. The levies paid is used for amongst others, payment for garden services, security, rates, water etc and for the common property.