I replaced these yellow blocks after the entire top was pieced. They used to be pink. I knew I wouldn't like the top if I didn't change them, so I carefully picked the pink ones out and replaced them with the yellow. I'm not sure about your log cabin, but I ended up using a Y Seam to get them back in, if I recall correctly.
If I was going to do it again, I would cut a new centre slightly larger than the old one, after backing it with something like Steam a Seam 2 Lite, fuse it directly over the one that was already there and then do a small buttonhole stitch around it with matching thread.
Watson