OK, I managed to fix it myself. Simply change the gem source from 26 60 01 80 to 5E 0D 03 80.

I'm trying to convert the radial gem from the Executioner at the start of the game into the Milkweed rune. Here's the original Executioner gem: 4D 04 B1 C0 \\ 26 60 01 80 \\ 01 00 00 00 \\ 01 00 00 00 5E ED 01 00 \\ FF FF FF FF \\ FF FF FF FF And this is how I changed it to the Milkweed rune: 4D 04 ...