Unfortunately I've had to do the same thing myself. You can extract that single block, reposition, and re-sew. I would suggest that you extend your ripped seams a little further than just the immediate block just to give yourself some wiggle room. I had one quilt that was sandwiched and partially quilted when I noticed one star block had points facing the wrong way! What a pain but was able to fix while everything was still together and continue on my merry way.