The ietf-nat@2018-02-23 introduces concept of polices (/nat/instances/instance/policy).
One of policy child nodes we currently support is nat64-prefixes.
VPP supports single prefix for given VRF. We currently map VRFs to NAT instances.
Therefore we can only support single policy per instance.
The draft-ietf-opsawg-nat-yang-14 permits such implementation:
Defining multiple NAT instances or configuring multiple NAT policies within one single NAT instance is implementation- and deployment- specific.