Ship Upgrade Confusion

So I have a Freelancer DUR with 6 months insurance. It also came with game package and SQ42.

Currently you can buy the Avenger with 120 months insurance.

If I exchange the DUR for store credit, can I then use that credit to buy the Avenger with 120 months insurance... do a ship upgrade back to DUR (again using store credit and some cash to cover the difference)... ending up back where I started but with 120 months insurance on the DUR?

Also I can do all this but keep the original SQ42 purchase as that is a separate exchange?