To my big surprise, OpenSIPS is not transparent in regards with route parameters. In route scripts, there is no easy way to copy all the route params from the incoming message into the outgoing ones.
I extended the RR modules in order to give access to rr params in a pseudo variable named $rr_params
So copying route params becomes easy
if (loose_route() )
record_route( $rr_params );
Examining and modifying route params beforehand in script variables or AVPs is also vastly simplified.