Active networks have been proposed to allow the dynamic extension of network behavior by downloading application-specific protocols (ASPs) into network routers. In this paper, we demonstrate feasibility of the use of ASPs in an active network for the adaptation of distributed software components. We have implemented three examples which show that ASPs can be used to easily extend distributed applications, and furthermore, that such adaptation can be safe, portable and efficient. Safety and efficiency is obtained by implementing the ASPs in PLAN-P, a domain-specific language and run-time system for active networking. The presented examples illustrate three different applications: (i) audio broadcasting with bandwidth adaptation in routers, (ii) an extensible HTTP server with load-balancing facilities, (iii) a multipoint MPEG server derived from a point-to-point server.