How to support multiple XML schemas in ASM?

I figured it out. Header-Based Content Profiles in the Allowed URL Properties:

Just enter multiple entries for (in my case) Content-Type as the Request Header Name and the different version tags go into the Request Header Value. Parse as XML, and use a different XML Profile with each. Each XML Profile has a different version .XSD attached to it. So, if the ASM sees HTTP header "Content-Type: application/com.foobar.api-v2+xml", it will use the provision_api_v2 profile which uses v2 of the XML XSD when parsing it.

Can be verified by the ASM request logs - if there is an XML schema violation and you click for details, it will list the XML Profile that was used when determining the violation: