--- ../src-base/minecraft/net/minecraft/client/gui/GuiCreateWorld.java
+++ ../src-work/minecraft/net/minecraft/client/gui/GuiCreateWorld.java
@@ -322,14 +322,7 @@
             }
             else if (p_146284_1_.field_146127_k == 8)
             {
-                if (WorldType.field_77139_a[this.field_146331_K] == WorldType.field_77138_c)
-                {
-                    this.field_146297_k.func_147108_a(new GuiCreateFlatWorld(this, this.field_146334_a));
-                }
-                else
-                {
-                    this.field_146297_k.func_147108_a(new GuiCustomizeWorldScreen(this, this.field_146334_a));
-                }
+                WorldType.field_77139_a[this.field_146331_K].onCustomizeButton(field_146297_k, this);
             }
         }
     }
@@ -381,7 +374,7 @@
             this.field_146326_C.field_146125_m = this.field_146344_y;
             this.field_146320_D.field_146125_m = this.field_146344_y;
             this.field_146321_E.field_146125_m = this.field_146344_y;
-            this.field_146322_F.field_146125_m = this.field_146344_y && (WorldType.field_77139_a[this.field_146331_K] == WorldType.field_77138_c || WorldType.field_77139_a[this.field_146331_K] == WorldType.field_180271_f);
+            this.field_146322_F.field_146125_m = this.field_146344_y && WorldType.field_77139_a[this.field_146331_K].isCustomizable();
         }
 
         this.func_146319_h();
