I was going to ask this on main site, but I am not sure if it is even possible. If someone thinks it is possible to solve, I can post an official question. Is it possible to write a macro (\renewcommand or such) so that this line
  \includegraphics[width=0.1\paperwidth]{images/1_pic}
is replaced by this
\ifdefined\HCode
  \includegraphics[width=0.1\paperwidth]{image.eps}
\else
  \includegraphics[width=0.1\paperwidth]{image.pdf}
\fi

If I use renewcommand, it will not work, since infinite loop results. i.e. I can't do this:
\renewcommand\includegraphics[2][]
{
\ifdefined\HCode
  \includegraphics[#1]{#2.eps}
\else
  \includegraphics[#1]{#2.pdf}
\fi
}

 (no author)  1
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 carlisle     2
 Chris       18
 david       15
 design       3
 Frank       18
 joseph    2835
 kastrup      4
 latex3     115
 mittelba   538
 morten     410
 Rainer       7
 robin        1
 rowley       1
 schoepf      7
 will       646

\RequirePackage{keyval}
\makeatletter
\define@key{foo}{bar}{\def\my@key@value{#1}}
\@namedef{my@key@string@A}{0}
\@namedef{my@key@string@B}{1}
\@namedef{my@key@string@C}{1}
% Process keys then
\ifcase\csname my@key@string@\my@key@value\endcsname\space
  % Code for first string
\or
  % Code for second string
\or
  % Code for third string
...
\else
  % Fall back
\fi

$ more l3format.log
This is pdfTeX, Version 3.14159265-2.6-1.40.16 (TeX Live 2015) (INITEX)  23 JUL
2015 23:43
 restricted \write18 enabled.
 %&-line parsing enabled.
**l3format.ins
(./l3format.ins (./l3docstrip.dtx)
Runaway definition?
{2012/06/08} \def \ExplFileName {l3docstrip} \def \ExplFileVersion {3\ETC.
! File ended while scanning definition of \ExplFileDate.
<inserted text>
                }
l.20 \input l3docstrip.dtx

palladium:l3kernel joseph$ texlua build.lua format

Transcript written on ../build/unpacked/l3format.log.
This is pdfTeX, Version 3.14159265-2.6-1.40.16 (TeX Live 2015) (INITEX)
 restricted \write18 enabled.
entering extended mode
(./l3format.ltx )
Beginning to dump on file l3format.fmt
 (preloaded format=l3format 2015.7.23)
7584 strings of total length 148529
79989 memory locations dumped; current usage is 37&79796
6047 multiletter control sequences
\font\nullfont=nullfont
0 words of font info for 0 preloaded fonts
0 hyphenation exceptions
Hyphenation trie of length 256 has 0 ops out of 35111

palladium:trunk joseph$ svn status
palladium:trunk joseph$ cd l3kernel/
palladium:l3kernel joseph$ texlua build.lua format
This is TeX, Version 3.14159265 (TeX Live 2015) (preloaded format=tex)
(./l3.ins (./l3docstrip.dtx (../local/docstrip.tex
Utility: `docstrip' 2.5d <2005/07/29>
English documentation    <1999/03/31>

**********************************************************
* This program converts documented macro-files into fast *
* loadable files by stripping off (nearly) all comments! *
**********************************************************

palladium:trunk joseph$ svn up
Updating '.':
At revision 5678.