Pierluigi,

Yes, you could do that with ip local policy route-map

The trick is to force the traffic re-enter the device and then catch it on its way out.

1.create an access list which matches the inteneded traffic or the entire traffic (do not try in production n/w)

2.create a loopback interface

3.under the route-map, set your interface as the created loopback and set the prec or dscp

4.Apply the ip local policy route-map to router.

HTH,