Hi Antero,
Yes, this is possible. Just check the link below for more details
http://www.cisco.com/en/US/docs/interfaces_modules/services_modules/ace/vA2_3_0/configuration/slb/guide/classlb.html#wp1151822
Assuming "http://www.xpto.com" is the only request you want to rewrite, the syntax of the action would be "header rewrite request Host header-value www.xpto.com replace xpto.com"
If, however, you need to create this action in a more generic way so that any URL is rewritten in the same format, you would need to use a regular expression. In this case, it would be something similar to the following (I didn't test it, so I'm not 100% sure that the regex is correct) "header rewrite request Host header-value www\.(.*)\.com replace %1.com"
I hope this helps
Daniel
