Possibly the easiest way to accomplish such a task would be to add a note to the Bill of Material in the Bill of Material Entry window. There is quite a bit of room in the Notes field for instructions.
Getting the notes to print on the desired report can be a little perplexing because the link is a bit convoluted. The notes text is stored in the Manufacturing Notes table [MN010000]. The Bill of Material Master Record is stored in the Bill of Material Header table [BM010415]. The Note Index is stored in the Item Engineering Data [IVR10015] able, so there can only be one Note for all Bill of Material (regardless of Category).
Here is a query to connect the data:
from BM010415 BH
-- BH is BOM Header BM010415
Left Join IVR10015 IED on BH.ITEMNMBR = IED.ITEMNMBR
-- IED is Item Engineering Data IVR10015
Left Join MN010000 MNF on IED.MFGNOTEINDEX_I = MNF.NOTEINDX
-- MNF is Manufacturing Note File MN010000
Left Join IV00101 IM on BH.ITEMNMBR = IM.ITEMNMBR
-- IM is Item Master IV00101
Where BH.ITEMNMBR = '100XLGA' and BH.BOMCAT_I = 1
-- BOMCAT_I = 1 is Manufacturing BOM
/* BOM Notes are linked to the BOM record through the Item Engineering Data Table (IVR10015)
The MFGNOTEINDEX_I field value maps to the NOTEINDX field in the Manufacturing Notes File MN010000*/