Why not try formatting General before pasting?

@ is the number format symbol to format the cell as Text.

And you're formatting any text in that cell so that's it's surrounded by ()'s.

But by copying a number and paste special|values, then excel sees the value as a
number--not Text.

By retyping the value, you're telling excel to see that value as text and the
number format will do its job.

Maybe you can be more specific and use a custom format of something like:
(General);(-General);(0);(@)

Then all the entries (positive, negative, 0 and text) will be surrounded by
()'s.  (I didn't need the double quotes, either.)

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This is kind of like when a cell is formatted as text and 123 is entered into
that cell.

Just changing the format won't change the underlying value back to a number.
Hitting F2, followed by enter (or reentering the value) will force excel to see
it as a number.