Hi Cameron,
Please check the documentation:
http://openser.org/docs/modules/1.2.x/uac.html#AEN160
Yes, it is possible to use AVPs within uac_replace_from().
For both 1.1 and 1.2:
http://openser.org/docs/modules/1.1.x/uac.html#AEN160
Thanks
Should have read the docs.
Cameron