how to redefine beamer template

Question

Until now I was not successful while trying to redefine a beamer template. In texwelt.de I found the hint to just use \setbeamertemplate, but this does not work.

\documentclass{beamer}
\usetheme{default}
\AtBeginDocument{%
\setbeamertemplate*{block example begin}
{
  \par\vskip\medskipamount%
  \begin{beamercolorbox}[colsep*=.75ex]{block title example}
    \usebeamerfont*{block title example}\insertblocktitle%
  \end{beamercolorbox}%
  {\parskip0pt\par}%
  \ifbeamercolorempty[bg]{block title example}
  {}
  {\ifbeamercolorempty[bg]{block body example}{}{\nointerlineskip\vskip-0.5pt}}%
  \usebeamerfont{block body example}%
  \begin{beamercolorbox}[colsep*=.75ex,vmode]{block body example}%
    \ifbeamercolorempty[bg]{block body example}{\vskip-.25ex}{\vskip-.75ex}\vbox{}%
}
}

\begin{document}
A
\end{document}

Answer 1

\AtBeginDocument is not necessary and the command to set a beamer template is \setbeamertemplate not \setbeamertemplate*. The following code works fine for me:

\documentclass{beamer}

\setbeamertemplate{block example begin}
{
  \par\vskip\medskipamount%
  \begin{beamercolorbox}[colsep*=.75ex]{block title example}
    \usebeamerfont*{block title example}\insertblocktitle%
  \end{beamercolorbox}%
  {\parskip0pt\par}%
  \ifbeamercolorempty[bg]{block title example}
  {}
  {\ifbeamercolorempty[bg]{block body example}{}{\nointerlineskip\vskip-0.5pt}}%
  \usebeamerfont{block body example}%
  \begin{beamercolorbox}[colsep*=.75ex,vmode]{block body example}%
    \ifbeamercolorempty[bg]{block body example}{\vskip-.25ex}{\vskip-.75ex}\vbox{}%
}

\begin{document}
\begin{frame}
\begin{exampleblock}{Example}
    Block content.
\end{exampleblock}
\end{frame}
\end{document}