Thanks Board gurus, you were right - block extraction is possible!
I just reversed exactly what I had done to sew that block in the first place: first, undoing the row-to-row seams and undoing a little extra on each side, then undoing just the block-to-block seams on each side of the bad block, and removed the block. Then I took out the threads, my most hated part of sewing. Ugh. 40-plus inches of threads. That all took about half an hour not counting complaining and groaning.
I starched the block that was upside down and the surrounding blocks, and re-sized and repressed the area to get the want-to-be-wonky triangles back in shape.
Then I sewed it all up in exactly the same way I had sewn it the first time (except not upside down haha). First I pinned the block to its neighbor on the left, and sewed and pressed. Ditto for the right side.
Then I had a condition similar to getting ready to sew the rows together, except that they are partly sewed already on each end. Match, pin, sew each row back together being sure to catch the already-sewn parts.
The pinning and sewing took about an hour.
Here are a couple shots of the operation - patient is recuperating at home.
Cut out the offending block
Cured wonky block and pinned to neighbor
side seams done - sewing rows
Finished quilt center