How do you specify a different port number in SQL Management Studio?

You'll need the SQL Server Configuration Manager. Go to Sql Native Client Configuration, Select Client Protocols, Right Click on TCP/IP and set your default port there.

Another way is to setup an alias in Config Manager. Then simply type that alias name when you want to connect. This makes it much easier and is more prefereable when you have to manage several servers/instances and/or servers on multiple ports and/or multiple protocols. Give them friendly names and it becomes much easier to remember them.

127.0.0.1,6283

Add a comma between the ip and port

If you're connecting to a named instance and UDP is not available when connecting to it, then you may need to specify the protocol as well.

Example: tcp:192.168.1.21\SQL2K5,1443