Note: The SQL Server Browser service records the port number on which each named instance is running on the computer in the Msmdredir.ini file (it records this the first time a user attempts to connect to the named instance, not when the named instance starts) and uses this information to direct client requests to connect to the named instance to the appropriate TCP port. To work properly, the SQL Server Browser service must run under a security account that has local administrator rights, such as the local system account. If a named instance is installed, the SQL Server Browser service is, by default, configured to start automatically.
How to change Port for SSAS Service (SSAS 2005 & SSAS 2008):
Non-clustered environment (Default Instance or Named Instance)
You can configure a named instance to run under a specified port by changing the Port property for the Analysis Services instance to a specified value by using SQL Server Management Studio (this is an advanced property) or by editing the Port server property (<Port>0</Port>) in Msmdsrv.ini file directly (in the ../OLAP/Config folder). A value of zero (the default value) means that Analysis Services dynamically assigns the port at startup
Note: To ensure that the new port information for the instance is relayed by the SQL Browser services to the client applications that are connecting to this instance ensure that the InstanceVisible property for the instance is set to 1. Otherwise you may experience connectivity issues from your client applications.
Clustered environment (Default Instance or Named Instance)
SSAS will start listening on all Public IP addresses of the cluster group using the default port (2383). Any alternate port configuration is ignored.