There are other codes for adding MSME numbers etc -- added in the Sales Invoice. You can search for the same and modify it for FSSAI.........
[#Part: EXPINV SaleSalesTax] add:Line:After:EXPINV PANITNumber:myfssai [Line:myfssai] Fields : Medium Prompt,fssainumber Local : Field : Medium Prompt : Set As : "Company's FSSAI Number:" ;Invisible : NOT @@CompanyPAN OR $$IsEmpty:$IncomeTaxNumber:Company:##SVCurrentCompany [Field:fssainumber] Set as :$FSSAINUMBER1:Company:##SVCurrentCompany Style : Normal Bold [#Part: PANCIN India] Add:Line:After: CMP CINumber: FSINumber [Line:FSINumber] Left Fields : Medium Prompt, CMPfssaiNumber Local : Field : medium Prompt : Set as : $$LocaleString:"Company's FSSAI No :" Option : Small Size Line [Field:CMPfssaiNumber] Use : Short Name Field Use : Upper Case Field Width : @@NameWidth Max : 21 Storage : FSSAINUMBER1 ASCIIOnly : Yes [System:UDF] FSSAINUMBER1:String:1001