Hello Avinash,
Sorry for some delay in response. I was also thinking, what's useful that I could tell you.
I understand your idea to shrink the image to 16MB, so that work around the bug which affects images >16MB. However, flashrom checks whether the size of the image is the same as the size of the chip (should throw an error if not). So to write 16MB onto GD25LR512ME which is 64MB, you would need to pad the file, with zeros usually, to make the file 64MB. I don't know whether it would work. Is it possible that you would try (if you have tools to recover your device from failure of course)? Or perhaps you have tried already?
On the other hand, some good news: support for chips GD25LR256E, GD251R512ME has been submitted meanwhile. So no need for patching anymore, the patch linked earlier in the thread is merged into main.