A network function modification method, system, and computer program product, include terminating the connection-oriented session between a client and a server via at least two proxies, running a multipath connection-oriented session between the at least two proxies, if an insertion request is received, establishing a first multipath subflow with the new multipath subflow traversing the network function of the insertion request, and if a removal request is received, establishing a second multipath subflow with the new multipath subflow not traversing the network function of the removal request.