Here's a rather magical two lines you can place at the top of your (single-file) latex file to preprocess it with and arbitrary stdin-stdout script (call your script foo.sh):
\input{|"cat \jobname.tex| sed -n '/^__END__/,$ p' | sed '1 d' | ./foo.sh"}
__END__
So for example let's say your tex file is:
\input{|"cat \jobname.tex| sed -n '/^__END__/,$ p' | sed '1 d' |
sed 's/[Cc]ensor[A-z]*/XXXX/g'"}
__END__
\documentclass{article}
\begin{document}
\section{Censorship}
Censor words starting with censor.
\end{document}
Then the output will be
Note: If you're using pdflatex you need to enable shell scripts by adding the --shell-escape argument.