Can you boost the tractored ship backward or only forward? Rule as written suggests only forward as it says perform a boost action using the 1 forward template and boosting cannot be done backward. Is this rule as intended?

Boost only goes forward.

Consider that inertia still applies in space. On a ship of similar mass, you'd have to absorb so much of their momentum to make them stop completely and go backwards. Basically, you pump the tractor beam, which pulls them slightly off course.