TBTR: Add option to replace only old vehicles

src/vehicle_cmd.cpp

@@ -899,6 +899,35 @@ CommandCost CmdToggleRefitAsTemplate(TileIndex tile, DoCommandFlag flags, uint32
 	return CommandCost();
 }
 
+/**
+ * Toggles replace old only on a template vehicle.
+ * @param tile unused
+ * @param flags type of operation
+ * @param p1 the template vehicle's index
+ * @param p2 unused
+ * @param text unused
+ * @return the cost of this operation or an error
+ */
+CommandCost CmdToggleTemplateReplaceOldOnly(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
+{
+	// Identify template to toggle
+	TemplateVehicle *template_vehicle = TemplateVehicle::GetIfValid(p1);
+
+	if (template_vehicle == NULL) {
+		return CMD_ERROR;
+	}
+
+	bool should_execute = (flags & DC_EXEC) != 0;
+
+	if (should_execute) {
+		template_vehicle->ToggleReplaceOldOnly();
+
+		InvalidateWindowClassesData(WC_TEMPLATEGUI_MAIN, 0);
+	}
+
+	return CommandCost();
+}
+
 /**
  * Create a virtual train from a template vehicle.
  * @param tile unused