Hej!
I changed the right part of the space bar to Ctrl by modifying Keyboard.c. The corresponding patch is:
diff --git a/reform2-keyboard-fw/Keyboard.c b/reform2-keyboard-fw/Keyboard.c
index 1dc1310..38aba7d 100644
--- a/reform2-keyboard-fw/Keyboard.c
+++ b/reform2-keyboard-fw/Keyboard.c
@@ -60,7 +60,7 @@ uint8_t matrix[COLS*6+2] = {
HID_KEYBOARD_SC_LEFT_SHIFT, HID_KEYBOARD_SC_NON_US_BACKSLASH_AND_PIPE, KEY_Z, KEY_X, KEY_C, KEY_V, KEY_B, KEY_N, KEY_M, HID_KEYBOARD_SC_COMMA_AND_LESS_THAN_SIGN, HID_KEYBOARD_SC_DOT_AND_GREATER_THAN_SIGN, KEY_SLASH_AND_QUESTION_MARK, HID_KEYBOARD_SC_UP_ARROW, HID_KEYBOARD_SC_RIGHT_SHIFT,
- HID_KEYBOARD_SC_RIGHT_GUI, HID_KEYBOARD_SC_LEFT_GUI, HID_KEYBOARD_SC_RIGHT_CONTROL, KEY_SPACE, HID_KEYBOARD_SC_LEFT_ALT, HID_KEYBOARD_SC_RIGHT_ALT, KEY_SPACE, HID_KEYBOARD_SC_PAGE_UP, HID_KEYBOARD_SC_PAGE_DOWN, HID_KEYBOARD_SC_LEFT_ARROW, HID_KEYBOARD_SC_DOWN_ARROW, HID_KEYBOARD_SC_RIGHT_ARROW, 0xfe,0xed,0xca,0xfe
+ HID_KEYBOARD_SC_RIGHT_GUI, HID_KEYBOARD_SC_LEFT_GUI, HID_KEYBOARD_SC_RIGHT_CONTROL, KEY_SPACE, HID_KEYBOARD_SC_LEFT_ALT, HID_KEYBOARD_SC_RIGHT_ALT, HID_KEYBOARD_SC_RIGHT_CONTROL, HID_KEYBOARD_SC_PAGE_UP, HID_KEYBOARD_SC_PAGE_DOWN, HID_KEYBOARD_SC_LEFT_ARROW, HID_KEYBOARD_SC_DOWN_ARROW, HID_KEYBOARD_SC_RIGHT_ARROW, 0xfe,0xed,0xca,0xfe
};
/** Buffer to hold the previously generated Keyboard HID report, for comparison purposes inside the HID class driver. */
But note that changing the actual keyboard firmware is not the only way you can change the keyboard mapping. I documented how I added a SysRq key on the OS level using udev which should also work for other keycodes: Remapping keyboard without firmware modification (adding SysRq key) - #3 by Chartreuse
To actually make use of the Hyper key as such (I think it acts by default as “right GUI/logo” key), you will also have to adjust the xkb config to map that modifier key. I haven’t written that part down yet but intend to do so soon.
Best of luck!