switchstyle1.tex

\documentclass[oneside]{report}

\usepackage{fancyhdr}
\usepackage{lipsum}
\usepackage{fancyhdr}
\usepackage{blindtext}

\pagestyle{fancy}
\fancyhf{}
\fancyhead[L]{\leftmark}
\fancyhead[R]{\rightmark}
\fancyfoot[C]{\thepage}


\fancypagestyle{special}{%
  \fancyhf{}
  \renewcommand{\headrulewidth}{0pt}
  \fancyhead[L]{Special Page Style \nouppercase\leftmark}
  \fancyfoot[R]{\thepage}
}

\begin{document}
\chapter{Introduction}

This example shows the effects of having the header and footer definitions \emph{global}, i.e. not embedded in the page style. The page style \texttt{special} does have some relevant definitions inside it, but the page style \texttt{fancy} doesn't. So when we change the page style to \texttt{special}, the header and footer definitions are overwritten, and when we switch back to page style \texttt{fancy} they are not reset, as \texttt{fancy} doesn't have them embedded.

\bigskip

\lipsum

\chapter{Special Chapter}
\pagestyle{special}
\lipsum

\chapter{Another Chapter}
\pagestyle{fancy}
\lipsum

\end{document}