you have to delete the BOM for the item to allow changing the Item Maintenance setting from KIT to Raw Material (or Finished Good). I have on occasion,
1. changed the BOM to Inactive, then
2. copied it to a ""new"" BOM with an Inactive Type.
3. changed the item master, from KIT to the new setting (RM or FG)
4. then created the BOM fresh as a Standard Type, copying from the ""new"" BOM I created in step # 2 above.
Seems like a ""lot of work""; because it is a lot of work.