If u have lots of stool (fecal loading) that's dry and hard, are u at higher risk for perforation if u bend down, do crunches, or contort the torso?

Probably not: Unless you have such severe fecal loading that you've basically developed an obstruction and subsequent severe intestinal dilation. And the high risk would be a blunt force trauma/"blow" to the belly rather then bending. If it's reached that point, you'll probably already be in the hospital or own your way there.

Consitipation: Hard stool is a stress on the rectum. It can cause the bowels to be stretched and possible traumatized while having a bowel movement. Extreme pressure on you abdomen, like crunches can help to put more pressure on that area. Increase your fluids, change your diet ( add prunes) and possible use a stool softener to help get your stools better, prior to engaging in that activity.