Etoolbox's patchcmd can't find search pattern due to hyperref package

hyperref has to define a great many internal commands to do its thing.

In this case the original definition of @chapter is saved to Hy@org@chapter by hyperref, @chapter is then redefined to do some linking and then calls Hy@org@chapter.

So the solution here is to patch Hy@org@chapter instead of @chapter when hyperref is loaded.

documentclass[12pt,twoside,openright]{report}

usepackage[utf8]{inputenc}
usepackage[T1]{fontenc}
usepackage[french]{babel}
usepackage{lmodern}
usepackage{microtype}

usepackage{etoolbox}

usepackage[pdftex,colorlinks,linkcolor=blue,citecolor=red]{hyperref}

%----------------------- Patch -----------------------
tracingpatches
makeatletter
patchcmd{Hy@org@chapter}%        
  {addtocontents{lof}{protectaddvspace{10p@}}}% <search>
  {addtocontents{lof}{protectaddvspace{15p@}}}% <replace>
  {}{}% <success><failure>
makeatother
%-----------------------------------------------------


begin{document}
listoffigures
chapter{A chapter}
begin{figure}caption{A figure}end{figure}
begin{figure}caption{A figure}end{figure}
chapter{A chapter}
begin{figure}caption{A figure}end{figure}
begin{figure}caption{A figure}end{figure}
appendix
chapter{A chapter}
addtocontents{lof}{protectaddvspace{10pt}}%
begin{figure}caption{A figure}end{figure}
begin{figure}caption{A figure}end{figure}
end{document}

gives

and

[debug] tracing patchcmd on input line 16
[debug] analyzing 'Hy@org@chapter'
[debug] ++ control sequence is defined
[debug] ++ control sequence is a macro
[debug] ++ macro can be retokenized cleanly
[debug] ++ search pattern found in replacement text
[debug] ++ patching possible
[debug] == retokenizing macro now

---

Alternatively, you can try to get your patch in before hyperref applies its redefinitions.

documentclass[12pt,twoside,openright]{report}

usepackage{etoolbox}

%----------------------- Patch -----------------------
tracingpatches
makeatletter
patchcmd{@chapter}%        
  {addtocontents{lof}{protectaddvspace{10p@}}}% <search>
  {addtocontents{lof}{protectaddvspace{15p@}}}% <replace>
  {}{}% <success><failure>
makeatother
%-----------------------------------------------------

usepackage[utf8]{inputenc}
usepackage[T1]{fontenc}
usepackage[french]{babel}
usepackage{lmodern}
usepackage{microtype}

usepackage[pdftex,colorlinks,linkcolor=blue,citecolor=red]{hyperref}



begin{document}
listoffigures
chapter{A chapter}
begin{figure}caption{A figure}end{figure}
begin{figure}caption{A figure}end{figure}
chapter{A chapter}
begin{figure}caption{A figure}end{figure}
begin{figure}caption{A figure}end{figure}
appendix
chapter{A chapter}
addtocontents{lof}{protectaddvspace{10pt}}%
begin{figure}caption{A figure}end{figure}
begin{figure}caption{A figure}end{figure}
end{document}

Thanks to David Carlisle for suggesting that in the comments.