Multiecuscan

Can I make this modification (6->1, 14->9) to interface permanent or shall I install a switch to change connection of CAN lines between pin 1 and 6 and 9 and 14? Will all modules be available in Grande Punto with modified interface or connection to engine management requires unmodified interface, while connection to power steering and service interval reset requires modified interface?

You cannot short circuit the two CAN buses.
You need either a switch to select either 1/9 or 6/14. Or you can use a patch cable.
And you cannot access all modules with only one cable. You need 6/14 for Engine and Power steering and 1/9 for dashboard, service reset, body computer.