THANKS A TON, PAMAURY!
If anyone wants to change the action of the volume buttons (while in Hold mode) to 'play/pause' and 'seek-back/skip-back', after applying pamaury's patch, in 'apps/keymaps/keymap-fuzeplus.c' there is a struct called 'button_context_wps_locked' on line 102. Change it to this:
static const struct button_mapping button_context_wps_locked[] = {
{ ACTION_WPS_PLAY, BUTTON_VOL_UP, BUTTON_NONE },
{ ACTION_WPS_SKIPPREV, BUTTON_VOL_DOWN|BUTTON_REL, BUTTON_VOL_DOWN },
{ ACTION_WPS_SEEKBACK, BUTTON_VOL_DOWN|BUTTON_REPEAT, BUTTON_NONE },
{ ACTION_WPS_STOPSEEK, BUTTON_VOL_DOWN|BUTTON_REL, BUTTON_VOL_DOWN|BUTTON_REPEAT },
LAST_ITEM_IN_LIST__NEXTLIST(CONTEXT_STD)