I am trying to replace the front brake pads and ran into the problem of getting the caliper piston to retract. I have tried just about everything and can't get it to budge. I have read through what I could find on here regarding this issue. My last attempt was using a C-clamp, old break pad and loosing the cap on the master cylinder but it still will not move. I do not think it is siezed because it looks like it moved out about a 1/4" while I was removing the old pads. As far as I can tell it looks straight and not binding. If I loosen the bleeder will that release the preasure on the piston? Will that force me to have to bleed the whole system?

Yes, loosening the bleeder valve will let you retract the piston. No you'll only have to bleed that caliper, not the whole system. That still leaves the primary question unanswered. Why won't it retract?

Tried to find the thread but can't. I recall someone running into a simular situation and if I recall correctly it was the flexible brake line that connects to the caliper. Apparently they can fail internally and act as a check valve, not allowing fluid flow. Might try flexing it more than you have been while applying pressure on the piston.

On some calipers you can't simply push the piston in, especially on ABS systems, you actually have to turn the piston a little a at a time. With some make/models there is actually a tool for this procedure. YMMV.