In the Future Improvements section on the linked blog post to the original mod it says "HS400 mode is supported by hardware but it's not currently supported by the sunxi-mmc drivers in the Linux kernel."

So it seems plausible that support for the faster HS200 mode (that's enabled by this mod) was added after the original devices shipped. Just a guess though.

If you do the mod and it causes issues, you can revert to the original DDR52 mode through software, assuming you didn't break anything while soldering.