1. A method in a computer system of operating a server with a plurality of clients, such that the server provides one of a plurality of services when requested by one of the clients, each of the services having common steps and a plurality of behavior pairs, each behavior pair including a first alternative behavior and a second alternative behavior, the first alternative behavior corresponding to a series of one or more steps designed to be executed when the requesting client is one of a selected group of clients, the second alternative behavior corresponding to a series of one or more steps designed to be executed when the requesting client is not among the selected group of clients, the requesting client having associated with it an aggregation of indications, each indication being in either a first state or a second state, each indication corresponding to a behavior pair of one of the services and indicating whether the first alternative behavior or the second alternative behavior should be provided to the requesting client, the indications created after the client is completed without modifying the client, the method comprising the steps of: for each of the clients, under control of the client, requesting one of the services from the server; and under control of the servers. executing the common steps of the requested service; and for each behavior pair of the requested service, checking the indication associated with the requesting client that corresponds to the behavior pair of the requested service; if the checked indication is in the first state, executing the series of steps of the requested service corresponding to the first alternative behavior; and if the checked indication is in the second state, executing the series of steps of the requested service corresponding to the second alternative behavior.