is it possible to do such operation with ipf/ipnat:

we have router/NAT withreal address 1.2.3.4 and local machine with
address 10.10.10.10.

if udp packet from 10.10.10.10 port 10000 goes to router, change it's
header to be from 1.2.3.4 port 1234 and route

if udp packet comes to 1.2.3.4 port 1234 change it's header to be to
10.10.10.10 port 10000 and route



something like hardwired NAT, one IP/PORT to one IP/PORT mapping.