This is the same as the newly-expanded Armos combo option, where for Statue (Center) and Spinning Tile combos, the NPC that is spawned is configurable on a per-combo basis by the user. This allows for the default shooting statue NPCs (Rock, Sword, etc.) to be used without taking up a screen enemy slot or messing up enemy spawn orders. This also allows for custom statue NPCs like the sword-triggered statues or Beamos from Z3, and the eye guards from Z4 which stop shooting after all enemies are defeated. This also allows for environmental flavour and variations of the spinning tiles, such as tiles, pots, and skulls. I was even going to use it for the crow enemies from Z3/Z4.
If there proves to be something messed up with the "Shooting Statues" flag and EWeapons, then a new combo type can be created ("Spawn NPC Once")