It's never a good idea to modify directly a .sty file; that said, classicthesis uses the titlesec package to format the sectional unit headings and, in particular, it uses
\titlespacing*{\chapter}{0pt}{1\baselineskip}{1.2\baselineskip}
to control the space before and after chapter titles, so you can simply change the third (space after) and fourth (space after) arguments according to your needs; you can do this in the preamble of your document without changing classicthesis.sty. A simple example:
\documentclass[11pt,a5paper,footinclude=true,headinclude=true]{scrbook}
\usepackage[linedheaders,parts,pdfspacing]{classicthesis} % ,manychapters
\usepackage{lipsum}
\titlespacing*{\chapter}{0pt}{*12}{*7}
\begin{document}
\tableofcontents
\chapter{Test Chapter One}
\section{A Section}
\lipsum[1-6]
\chapter{Test Chapter One}
\lipsum[1]
\section{A Section}
\lipsum[1]
\end{document}
Of course, instead of the values I used (refer to the documentation for titlesec) you can use any valid length.
If the changes in spacing must apply only to numbered chapters, instead of using \titlespacing, a solution using \titleformat to discriminate between numbered and unnumbered chapters (with the help of the numberless key) can be used; in the following code I illustrate this approach in the case of the lineheaders option; for numbered chapters a space of 8\baselineskip was added before the title and 2\baselineskip was added after the tile; unnumbered chapters maintain their original settings:
\documentclass[11pt,a5paper,footinclude=true,headinclude=true]{scrbook}
\usepackage[linedheaders,parts,pdfspacing]{classicthesis} % ,manychapters
\usepackage{lipsum}
\titleformat{\chapter}[display]%
{\vspace*{8\baselineskip}}{\raggedleft{\color{halfgray}\chapterNumber\thechapter} \\ }
{0pt}{\titlerule\vspace*{.9\baselineskip}\raggedright\spacedallcaps}
[\normalsize\vspace*{.8\baselineskip}\titlerule\vspace*{2\baselineskip}]
\titleformat{name=\chapter,numberless}[display]%
{\relax}{}
{0pt}{\titlerule\vspace*{.9\baselineskip}\raggedright\spacedallcaps}
[\normalsize\vspace*{.8\baselineskip}\titlerule]
\begin{document}
\tableofcontents
\chapter{Test Chapter One}
\section{A Section}
\lipsum[1-6]
\chapter{Test Chapter One}
\lipsum[1]
\section{A Section}
\lipsum[1]
\end{document}
Add \leavevmode before the \color command.
(See a footnote about this in the grfguide documentation of colour support in LaTeX. (Sorry, its not my fault:-)
There is a different type of problem that will occur for all drivers.
Due to certain technical difficulties\footnote{At least two causes: 1)
The presence of a \texttt{\char`\\special} \m{whatsit} prevents
\texttt{\char`\\addvspace} ‘seeing’ space on the current vertical
list, so causing it to incorrectly add extra vertical space. 2) A
\m{whatsit} as the first item in a \texttt{\char`\\vtop} moves the
reference point of the box.}%
\documentclass[paper=a4,fontsize=11pt,BCOR=5mm,twoside,open=right,titlepage,
headinclude,footinclude,captions=tableheading,numbers=noenddot,fleqn,
cleardoublepage=empty]{scrreprt}
\usepackage[pdftex]{hyperref}
\usepackage[smaller,printonlyused,withpage]{acronym}
\usepackage[dvipsnames,svgnames,x11names,table,fixpdftex,hyperref]{xcolor}
\usepackage[eulerchapternumbers,eulermath,beramono,pdfspacing,linedheaders]{classicthesis}
\usepackage{arsclassica}
\renewcommand{\bflabel}[1]{{#1}\hfill}
\renewcommand*{\acsfont}[1]{\textsmaller{\textsf{\textsc{\textbf{\color{webgreen}{#1}}}}}}
\renewcommand*{\acffont}[1]{\textsf{\textsc{\color{webgreen}{#1}}}}
\areaset[current]{336pt}{750pt}
\setlength{\marginparwidth}{7em}
\setlength{\marginparsep}{2em}
\pdfcompresslevel=9
\pdfadjustspacing=1
\hypersetup{
colorlinks=true, linktocpage=true, pdfstartpage=3, pdfstartview=FitV,%
breaklinks=true, pdfpagemode=UseNone, pageanchor=true, pdfpagemode=UseOutlines,%
plainpages=false, bookmarksnumbered, bookmarksopen=true, bookmarksopenlevel=1,%
hypertexnames=true, pdfhighlight=/O,%nesting=true,%frenchlinks,%
urlcolor=webbrown, linkcolor=RoyalBlue, citecolor=webgreen, %pagecolor=RoyalBlue,%
pdftitle={The Title},%
pdfauthor={\textcopyright\ Stefano},%
pdfsubject={},%
pdfkeywords={},%
pdfcreator={pdfLaTeX},%
pdfproducer={LaTeX with hyperref and classicthesis}%
}
\makeatletter
\def\graffito@setup{%
\slshape\footnotesize% <=== I'm going to add \color{black} right here!
\leavevmode\color{black}%
\parindent=0pt \lineskip=0pt \lineskiplimit=0pt %
\tolerance=2000 \hyphenpenalty=300 \exhyphenpenalty=300%
\doublehyphendemerits=100000%
\finalhyphendemerits=\doublehyphendemerits}
\makeatother
\begin{document}
Best Answer
Copy the code from line 81 to 146 inclusive of
arsclassica.styand paste it into your preamble, removing all\sffamilycommands.Remove the setting to
\descriptionlabel, which is in that part of the code, but really doesn't belong there, and redefine\chapterNumber.If all you want is changing the chapter headings, remove all that doesn't refer to chapters.
Here's the reduced version: