The domain.xml file controls the port on which the server listens, not the port to which the asadmin client connects. To change the asadmin connect port, use the --port option.
For example, in your case, do:
$ asadmin --port 4242
Use "exit" to exit and "help" for online help.
Remote server does not listen for requests on [localhost:4242]. Is the server up?
Unable to get remote commands.
Closest matching local command(s):
Command start failed.