Which release? In 10.1 it is in <Windchill>/codebase/wvs.properties. In 10.2 it is in <Windchill>/codebase/WEB-INF/conf/wvs.properties.
Use xconfmanager to set it. For example
start a windchill shell
xconfmanager -p -t codebase/wvs.properties -s <somekey>=<somevalue>
or
xconfmanager -p -t codebase/WEB-INF/conf/wvs.properties -s <somekey>=<somevalue>