1. I don't think you can. If you delete the segments, then the router can go into diff. pair mode by selecting the connection. Otherwise, this is where you need to play with the stretch command. In that mode, you can move one of the routes towards the other, the diff. pair spacing is maintained, and you can adjust the length depending on which direction you stretch. You can also route one half to the needed length, then the other half to get close, and use the stretch command to push them back together. This can also affect the rest of the routing if you're not careful, so protect the sections you want to keep.The move command does not work here.
2. Set the spreadsheet view to look at pin-pairs.