Your doubleclick (enh.attribut editor) can edit Attributes, Attributes are part of Blockreferences, not part of a block.
Your (none constant) Attributdefinitions inside your Block are just templates for Attributes for new inserts.
Constant Attributdefinitions are not more like a Text or Mtext in a Block,
so the right way to edit is BEDIT.
And now you can re-think about your choice:
Would you also use Text(inside the Block) for projectname and adress?
If your answer is No, because of..
then constant attribut definitions are not the best choice for you.
Difference between Text an const.Attdef: You can extract constant attdefs, thats all.