Frankly Detlef, i think you did a great job with your restoration. First of all, we all know that sheaths will often be changed in the lifetime of a blade. So if one can restore the old sheath like you did or even create a brand new one from scratch as Jose did in the link you provide i see no real problem with that. It is just respectful to the blade to provide it with a good home.
My concern arises when we consider making physical changes to the blade such as with Ariel's example. Adding a new plate onto the blade requires a great deal of guess work and pretty much changes the blade forever.
