How do I change the footer/footline of a single frame in Beamer?

Question

So basically I've got something like this at the top of my tex file:

\setbeamertemplate{footline}{Number \insertframenumber}

This applies "Number <#>" to the footer/footline of all frames. Now what I want to do is change the footline for one single frame. Surprisingly, the following doesn't work:

\begin{frame}
    \setbeamertemplate{footline}{New template \insertframenumber}
\end{frame}

How do I achieve changing the footline/footer for one single frame?

Solution

Thanks Thomas! For anyone else who might want to get this working, here's a complete example:

\documentclass{beamer}
\setbeamertemplate{footline}{goo \insertframenumber}

\begin{document}
    \begin{frame}[t]{Frame 1}
        A
    \end{frame}

    { % these braces make the change local to the single frame
        \setbeamertemplate{footline}{boo \insertframenumber}
        \begin{frame}[t]{Frame 2}
            B
        \end{frame}
    }

    \begin{frame}[t]{Frame 3}
        C
    \end{frame}
\end{document}