The issue here is you are probaly using the IOS-XR CLI NED that models a route policy as a name and a single leaf with the policy definition. If the policy definition has a structure and different services for example can add a 'match' in the policy, then the way to do this is to have a service dedicated to managing the route policy. You model that service as you need, for exampl with a leaf-list of matches. The create callback of your services goes through the list of matches and build the required policy string.
Then the services that require a match to be added, specify that match in the template by adding a match under the service that manages the route policy. That's an example of the stacked services pattern, where the template of a service is specifying what it's intent is, in terms of a lower level service.
