This would be very helpful on many many ocassions:

Imagine you're editing a code:

class Foo {
  String path;

  setPath( String path ){
      this.path = path;
  }
}

Then you decide to change path to Path.

      this.path = Paths.get(path);

So you set the cursor to 
      this.path = |path;

But, when writing the parenthesis, NetBeans will auto-complete:

      this.path = Paths.get(null)path;

So you actually have to delete the "null)" part and fix it.

It would be very convenient if in situations like this (i.e. method has 1 parameter of the type of the variable right after the cursor), NetBeans would  put the closing parenthesis after the variable.

It would also enter that "edit expression in a box" when you can change that, and if rewritten, the original variable would appear again after closing parentheses. But if accepted (i.e. enter pressed), it would stay in.

I hope I described it clearly :)
Thanks for considering.