Creating custom field while creating an 'Item' - Manufacturing module

Hi, we introduced ERPNext in our Manufacturing facility recently, and we’ve been trying to integrate it with our processes. For MRP purposes, we have classified all our inventories into two categories: long lead time inventories and short lead time inventories (fasteners and hardware). For short lead-time items, we have a Kanban Bin system and we want to exclude them in the Material Requirement Planning. How do we proceed with that? Is there an option to differentiate inventories and exclude them in MRP? Any leads would be appreciated. Thank you!