I don't understand how you imagine that could work. A hyperlink is a point
in your document that is linked to a specific destination. If you make a new
hyperlink it is another point in your document. It can't be the same point.
The first thing you would lose would be the ability to go to a hyperlink
from the hyperlinks palette: InDesign wouldn't know which of the identical
hyperlinks you wanted to find. Then what would happen if you removed a
hyperlink? Would that remove all identical hyperlinks?
As Dave points out, you can format hyperlinks in groups so the only
'problem' you have is a long listing in the hyperlinks palette, and I accept
that that can be a problem because in my experience InDesign can slow down
dramatically when it has to seek and identify a hyperlink every time you
select it with the text tool. But that's easily overcome by just rolling up
the palette and only opening it when you want to work with hyperlinks.
k