Changing value of uname -r

[Robert Bonomi]

> From owner-freebsd-questions at freebsd.org  Tue Jan  1 11:52:49 2013
> Date: Tue, 01 Jan 2013 12:49:17 -0500
> From: Fbsd8 <fbsd8 at a1poweruser.com>
> To: FreeBSD Questions <freebsd-questions at freebsd.org>
> Subject: Changing value of uname -r
>
> uname -r   returns 10.0-CURRENT
>
> setenv UNAME_r "9.0-RELEASE"
>
> uname -r   now returns 9.0-RELEASE
>
> How to reset uname -r to original value without doing
> setenv UNAME_r "10.0-CURRENT"?
>
> Is there some way just to deactivate the effect of the
> setenv UNAME_r so it returns to the real value of the system?

Did you try:
  unsetenv UNAME_r

If yes, what were the results?

If no, _why_not_?