No change to the shock is necessary. Even with the completely stock shock the improvements will be very noticeable.
We recommend air or coil shocks with this link. If you already have something installed on your bike and don’t feel like replacing it there certainly isn’t any reason to.
This link delivers substantially more bottom out resistance than the stock link. Using 28% to 32% sag should be your starting point. If you feel you need a little more first try adding a few clicks of damping to account for the change in leverage curve. If you still want even more you can try going up 10-20 psi in air shock pressure or 50lb in spring rate.
At 30% sag this link will also deliver much better small bump sensitivity so start there. If you still feel like you’d like a little more try running less damping. The link makes it so the suspension doesn’t rely on damping as much to avoid bottom outs so running less isn’t an issue.
The link keeps the bike's geometry the same as with the stock link.
Your best bet is to give Giant a call and ask them directly. Only they can make that decision.