Even though we bought a specific week, can we exchange for any time available at another Westin Vacation Club?

Keep in mind it the St. John resort is highly sought after so you are better off renting the unit and using the points for another Westin resort. This way you have the cash and the points which is a better deal for you.

Yes. If you bought from Developer (Vistana - previously Starwood) at any of the WSJ phases, or bought resale at VGV phase. You can use the StarOptions (Home Resort Options, aka points) to book anywhere within the network (VSN) at 8 months out.

It would be best to contact Westin ownership services directly to find out what your options are for exchanging.