the ability to pass a request from the client and augment the renderer server side was added at ArcGIS Server 10.1
Map services allow clients to change layer appearance and behavior dynamically...
http://resources.arcgis.com/en/help/main/10.1/#/What_s_new_in_ArcGIS_Server/016w00000036000000/
About dynamic layers
http://resources.arcgis.com/en/help/main/10.1/00sq/00sq000000n1000000.htm