Try going into the config files and change the existing JBossAdmin role to be ga-JBossAdm. For example, in the jmx console web.xml:
<security-constraint>
<web-resource-collection>
<web-resource-name>HtmlAdaptor</web-resource-name>
<url-pattern>/*</url-pattern>
<http-method>GET</http-method>
<http-method>POST</http-method>
</web-resource-collection>
<auth-constraint>
<role-name>ga-JBossAdm</role-name>
</auth-constraint>
</security-constraint>
<security-role>
<role-name>ga-JBossAdm</role-name>
</security-role>