Network Functions Virtualization (NFV) enablesthe complete decoupling of network functions from proprietaryappliances and runs them as software applications on general–purpose servers. Service Function Chains (SFC) are paths with anordered sequence of network functions that have to be processed.In this paper, we consider the problem of reconfiguring SFCswith the goal of bringing the network from a sub-optimal toan optimal operational state. We propose optimization modelsbased on themake-before-breakmechanism, in which a new SFCis set up before the old one is torn down. Our method takes intoconsideration the chaining requirements of the flows and scaleswell with the number of nodes in the network. We show that,with our approach, the network operational cost defined in termsof both bandwidth and installed network function costs can bereduced and a higher acceptance rate can be achieved.