Further OSM improvements:

locking support (double-tap to lock, tap to unlock or use KC_NO)
 includes word-lock (shift-lock: ' ' -> _)

keyboards/splitkb/kyria/rev3/keymaps/bluepython508/keymap.c

@@ -13,7 +13,7 @@
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
-#include "keycodes.h"
+#include "action.h"
 #include QMK_KEYBOARD_H
 
 enum keycodes {
@@ -204,6 +204,7 @@ typedef enum {
     os_up_queued,
     os_down_unused,
     os_down_used,
+    os_locked
 } oneshot_state_t;
 
 oneshot_state_t oneshot_state[4] = {0};
@@ -227,30 +228,44 @@ bool is_oneshot_ignored_key(uint16_t keycode) {
 
 bool is_oneshot_cancel_key(uint16_t keycode) {
   switch (keycode) {
-    case NAV:
-    case SYM:
-    case NUM:
-    case FUN:
+    // case NAV:
+    // case SYM:
+    // case NUM:
+    // case FUN:
+      // return true;
+    case KC_NO:
       return true;
     default:
       return false;
   }
 }
-// From https://github.com/qmk/qmk_firmware/blob/user-keymaps-still-present/users/callum/oneshot.c
+
+// Based on https://github.com/qmk/qmk_firmware/blob/user-keymaps-still-present/users/callum/oneshot.c
 void update_oneshot(
   oneshot_state_t *state,
   uint16_t mod,
   uint16_t trigger,
   uint16_t keycode,
   keyrecord_t *record
-) {
+  ) {
   if (keycode == trigger) {
     if (record->event.pressed) {
       // Trigger keydown
-            if (*state == os_up_unqueued) {
+      switch (*state) {
+        case os_up_queued:
+          *state = os_locked;
+          break;
+        case os_up_unqueued:
           register_code(mod);
-            }
           *state = os_down_unused;
+          break;
+        case os_locked:
+          *state = os_down_used;
+          break;
+        default:
+          *state = os_down_unused;
+          break;
+      }
     } else {
       // Trigger keyup
       switch (*state) {
@@ -299,6 +314,15 @@ bool process_record_user(uint16_t keycode, keyrecord_t *record) {
   update_oneshot(&oneshot_state[2], mods[2], OS_LALT, keycode, record);
   update_oneshot(&oneshot_state[3], mods[3], OS_LGUI, keycode, record);
 
+  if (oneshot_state[0] == os_locked && keycode == KC_SPACE) {
+    if (record->event.pressed) {
+      register_code(KC_MINUS);
+    } else {
+      unregister_code(KC_MINUS);
+    }
+    return false;
+  }
+
   return true;
 }