If I change my shackle angle...

if i change my shackle angle/mounting location to get leaned forward and lower a bit how will this change my pinion angle? if at all will it point more up or down?
thanks

Could be either or. Depends where the leaf spring eye ends up. If you just lower the shackle mounting point, the pinion will be pointed more up. If you just bring the mounting point forward resulting in a more extreme shackle angle, then the leaf spring eye will be higher than it was, and pinion angle will point further down.

Absolutely. If the rear support point is longer or shorter, the pinion angle is affected.

The more length/height you add shackle side, the more the pinion will be pointing upwards. You can easily counter this with shims, if the angle is not good...