5.6 Adding tex4ht configuration inside latex file instead of using .cfg

One can use \Configure after \begin{document}

These are from Michal Hoftich.

(untested, just an idea): 
 
\documentclass{article} 
\ifdefined\HCode 
\newcommand\html[1]{% 
\HCode{#1}% 
}% 
\else 
\newcommand\html[1]{}% 
\fi 
\begin{document} 
\html{<div class="hello>world</div>} 
\end{document}
 

And

You don't need \Preamble and \EndPreamble in your document, they are 
useful only in config file. You can use \Css, \Tg or \ConfigureEnv, 
but only after '\begin{document}'. Something like this should work: 
 
\documentclass{article} 
\usepackage{somepackage} 
\begin{document} 
 \ifx\HCode\undefined \else 
 \Css{body{background-color:green;}} 
 \ConfigureEnv{quote}{\Tg<quote>}{\Tg</quote>}{}{} 
 \fi 
 
\ifx\HCode will ensure that this code run only when tex4ht is loaded.