JSONizing mapgen_basement_junk gun safe items, any advice?

Modifying this bit of code in src/mapgen_functions.cpp mapgen_basement_junk:

if( one_in( 1600 ) ) { m->furn_set( p, furn_str_id( "f_gun_safe_el" ) ); if( one_in( 2 ) ) { m->spawn_item( p, "9mm", 2 ); m->spawn_item( p, "usp_9mm" ); m->spawn_item( p, "suppressor" ); m->spawn_item( p, "cash_card", 2 ); } else { m->place_items( "ammo", 96, p.x, p.y, p.x, p.y, false, 0 ); m->place_items( "guns_survival", 90, p.x, p.y, p.x, p.y, false, 0 ); } }
So far it looks like this:

if( one_in( 1600 ) ) { m->furn_set( p, furn_str_id( "f_gun_safe_el" ) ); if( one_in( 2 ) ) { m->place_items( "basement_op_guns", 96, p.x, p.y, p.x, p.y, false, 0 ); } else { m->place_items( "ammo", 90, p.x, p.y, p.x, p.y, false, 0 ); } }
With the new itemgroup in /itemgroups/locations.json:

  {
    "id": "basement_op_guns",
    "type": "item_group",
    "//": "Hardcoded gunsafe itemgroup for basement_junk in mapgen_functions.cpp .",
    "magazine": 100,
    "items": [
      {
        "distribution": [
          {
            "collection": [
              { "item": "usp_9mm" },
              { "item": "usp9mag" },
              { "item": "9mmP", "charges-min": 24, "charges-max": 50 },
              { "item": "suppressor" },
              { "item": "holster" }
            ], "prob": 20
          },
          {
            "collection": [
              { "item": "usp_9mm" },
              { "item": "9mm", "charges-min": 50, "charges-max": 50 },
              { "item": "suppressor" },
              { "item": "cash_card" }
            ], "prob": 50
          },
          {
            "collection": [
              { "group": "guns_pistol_milspec" },
              { "item": "holster" }
            ], "prob": 50
          },
              { "group": "guns_survival", "prob": 50 },
              { "group": "ammo", "prob": 50 }
        ]
      }
    ]
  },

Have I done anything gamebreaking?