Hi Cambler,

sorry for the delay in responding.
You can set a default this way:

1 - set the overall default template in the usual Joomla way using the template manager, if you need to.
2 - Chameleon rule 1: detect example.com and www.example.com as domain names, and in the succeed action set that template, AND continue to next rule.
3 - Chameleon rule 2: detect example.net and www.example.net as domain names, and in the succeed action set that template, AND continue to next rule.
4 - set up more Chameleon rules to detect individual menu items in combination with domain name example.com and www.example.com, and in the succeed action set the new template
5 - set up more Chameleon rules to detect individual menu items in combination with domain name example.net and www.example.net, and in the succeed action set the new template

When selecting menu items in this way, you can select multiple items using the chooser, and the rule will trigger when the visitor is on any one of them.