Tried lowering the car today on stock bolts. Backs went fine and i left 3 threads showing. The fronts gave me a lot of problems. I tried turning the bolts would not move. Then i tried putting jack stands under the leaf springs to relieve some tension and the bolt still wouldn't turn. The bolt looks really rusty and the top is rounded off. Even tried using tools that are meant to take off stripped bolts and still nothing. Does anybody have any suggestions? How hard is it to replace the bolt with a new one? Let me know.

 

Just an FYI:
Not sure if you know this, but those fronts bolts are reverse threaded (turn the opposite direction that you would normally expect).

Also, they are easily removed and replaced.

 

It sounds like someone has already tried to lower or raise the car at some point and also experienced the stuck bolts or vulcanized bushings on the lower control arm. If you do it right, you should be able to turn the bolts by hand w/o a wrench or socket, but it takes some preparation and patience. Replacement of the oem front bolts can be done, but you really need to drop the lower control arm and remove the spring for R&R of the bolts/bushings. You cannot buy the oem bolts/bushings from GM, but you can buy after market from a site supporting vendor called HARDBARUSA. You might also get lucky and find a member who has removed theirs for whatever reason. You could place an ad in the classified section.
If you do a search in C5 General, there was a recent discussion about a member who replaced his C5/Z06 front bolts/bushings with C6/Z06 bolts/bushings. It wasn't an easy job and the results were not what he expected...maybe because of the BILSTEIN shocks he has on his car.
Use PB BLASTER on the bolts first. On the top of the spring, there is a little trough around the bolt threads where it protrudes. Spray the product onto the threads and allow it to sit for a while (patience and preparation). Let it pool in that little trough. Don't spray on the threads directly above the bushings. When you see the product coming through the spring onto the threads above the bushing, you'll know it's thoroughly penetrated through the spring. The bolts can rust and trying to gorilla them out w/o preparation can strip the threaded inserts in the fiberglass spring. Then you'll have to replace the spring.
Chances are you will find the front bushing vulcanized to the lower control arm. So, when you attempt to adjust the bolt, the bushing will not easily turn. It'll reverse back to the same position after tension on the wrench/socket is eased.
You can use the same PB BLASTER that you use on the bolt threads on the bushings. Use a flat blade putty knife to pry the bushing away from the control arm. Once it's loose, you should be able to adjust the bolts/bushings by hand w/o a 10mm wrench/socket. Since the hex is rounded in your case, a large set of VICEGRIPS should work. You could weld an SAE nut onto the top of the damaged area and make it easy on yourself. Lubricate the bottom of the bushings with grease so they don't vulcanize to the lower control arm in the future.
The bolts are regular RH thread not LH thread, but if you don't watch closely what you're doing during the adjustment procedure, it's easy to get confused and adjust the front higher rather than lower.