After a lot of trials and errors I found easy solution, which is OK for me. In module_scene_props.py instead of
# we has a sappeur :3
(troop_slot_eq,":troop_id",slot_troop_class,multi_troop_class_mm_sapper),
paste
# we has a sappeur :3
(this_or_next|troop_slot_eq,":troop_id",slot_troop_class,multi_troop_class_mm_sapper),
(troop_slot_eq,":troop_id",slot_troop_class,multi_troop_class_mm_infantry),
Or add all troop_classes you want (copy first line, of this code, paste it over last line, and instead of multi_troop_class_mm_sapper write your troop class)
I hope, it will help somebody and save time :)