とりあえずVer.2.13までのお話で。
今後のVer.Upで変わるかもしれませんので要確認。

選択可能単位は『g』『kg』……未記入の場合『g』とされます。

さて、この項目を使用する際の注意事項を挙げてみましょう。

・子部品にのみ適用可能（製品データには適用できない）
■　　g←ココに適用できない
├■　kg
└■　g


・材料には適用できない
■　　　g
├■　　g
│├●　g
│└●　g
└■　　kg
　├●　g
　└●　g

例によって例の如く実際に再現してみました。

"C","Ver.2.13","2011/06/16","正常終了","","EXLIST-2011-06-01JP.xls"
"H","","","","",""
"D","1","dummy","dummy","3","","","1","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","",""
"D","2","dummy","dummy","","","","2","dummy1","dummy1","1","1","","Iron/Other Iron alloy (Unalloyed, low alloyed)","","1","JAMAA4444","FE1","","1.1.1","1","","","","7439-89-6","Iron","100","","0","0","0","0","","","","","","","","","","","","","","","","1762",""
"D","3","dummy","dummy","","","","2","dummy2","dummy2","0.001","2","","Iron/Other Iron alloy (Unalloyed, low alloyed)","","1","JAMAA4444","FE2","","1.1.1","1","","","","7439-89-6","Iron","100","","0","0","0","0","","","","","","","","kg","","","","","","","","1762",""

上の"C"からの文字列をtxtファイルに貼り付けて"C"・"H"・"D"で始まる5行に整形して保存→拡張子をcsvに変更してJAMAシートで取り込めます。

■dummy(3g)
├■dummy1(1g)*1
│└●FE1(1g)
└■dummy2(0.001kg)*2
　└●FE2(1g)

って構成なんですが、結果として構成中の子部品のみにしか適用できないわけです。

製品質量：g(固定)
構成部品質量：g or kg
材料質量：g(固定)

何がやりたいのかさっぱりわかりません。
コレって使い道あるのか？