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,