Replacing patches means taking apart part of the blocks, removing one patch and sewing a new one in. The chunks where a patch is missing look like the photo right. When a patch has been removed, it is just a hole. This is the way I have always removed patches. I try and remove as few seams as possible.
The yellow arrow points to the spot where I have removed a patch. I know it is a little hard to see in the photo above. The piecing looks totally normal except for the removed piece. It actually looks like there is a white piece of fabric in it.
The process isn’t difficult, but it is time consuming. I am also fixing seams, if I have the chance. Some of them seem to have something wrong with them and I may as well deal with them now.