change .bst file to get journal name bold

You could redefine the \APACjournalVolNumPages command (this is the formatting command that apacite.bst uses to format journal articles; see page 41 of the current (v6.03) manual):

\makeatletter
\renewcommand{\APACjournalVolNumPages}[4]{%
  \textbf{\Bem{#1}}%             journal
  \ifx\@empty#2\@empty
  \else
    \unskip, \Bem{#2}%  volume
  \fi
  \ifx\@empty#3\@empty
  \else
    \unskip({#3})%      issue number
  \fi
  \ifx\@empty#4\@empty
  \else
    \unskip, {#4}%      pages
  \fi
}
\makeatother

Thanks to Alan Munn for catching my missing \makeatletter-\makeatother. Also, see the second part of nickie's answer for a more elegant implementation of this approach.

Edit: Alternatively, and more in the spirit of your question, you could modify the .bst file to achieve the same result:

FUNCTION { format.journal.vol.num.pages.check }
{ "journal" journal warning.if.empty
  duplicate$ empty$
  journal    empty$ and
  volume     empty$ and
  number     empty$ and
    { pop$ "" }
    { "\APACjournalVolNumPages{\textbf{" journal "" connect.check
      "}}{" *                     volume  "" connect.check
      "}{" *                     number  "" connect.check
      "}{" *                     swap$   "" connect.check
      "}"  *
    }
  if$
}

To answer your second question, the journal name is italicized by default because it is formatted with the \Bem command, which is \let to be \emph in apacite.sty.

Result (same for either approach, using your modified myapacite.bst):

myapacite with bold journal names

Full MWE (with first option and unmodified myapacite.bst):

\documentclass[12pt]{scrartcl}

\begin{filecontents}{mwe.bib}
% This file was created with JabRef 2.11.1.
% Encoding: UTF8

@Unpublished{Ham2015,
  Title                    = {Narcissism and Financial Reporting Quality},
  Author                   = {Charles Ham and Mark H. Lang and Nicholas Seybert and Sean Wang},
  Note                     = {Available at SSRN: http://ssrn.com/abstract=2581157 or http://dx.doi.org/10.2139/ssrn.2581157},
  Year                     = {2015}
}

@Article{Ham2013,
  Title                    = {Narcissism is a Bad Sign: {CEO} Signature Size, Investment, and Performance},
  Author                   = {Ham, Charles and Seybert, Nicholas and Wang, Sean and Lundblad, Justin Leiby and Sevilir, Merih and Tate, Geoff and Williams, Devin and Zarowin, Paul and Zheng, Yue},
  Journal                  = {UNC Kenan-Flagler Research Paper},
  Year                     = {2013},
  Number                   = {2013-1},
  Type                     = {Journal Article}
}

@Article{Wink1991,
  Title                    = {Two faces of narcissism},
  Author                   = {Wink, Paul},
  Journal                  = {Journal of Personality and Social Psychology},
  Year                     = {1991},
  Number                   = {4},
  Pages                    = {590},
  Volume                   = {61},
  ISSN                     = {1939-1315},
  Type                     = {Journal Article}
}
\end{filecontents}

\usepackage{apacite}
\makeatletter
\renewcommand{\APACjournalVolNumPages}[4]{%
  \textbf{\Bem{#1}}%             journal
  \ifx\@empty#2\@empty
  \else
    \unskip, \Bem{#2}%  volume
  \fi
  \ifx\@empty#3\@empty
  \else
    \unskip({#3})%      issue number
  \fi
  \ifx\@empty#4\@empty
  \else
    \unskip, {#4}%      pages
  \fi
}
\makeatother
\begin{document}
blablabla    
\cite{Ham2013}
\cite{Ham2015}
\cite{Wink1991}

\bibliographystyle{myapacite}
\bibliography{mwe}
\end{document}

Edit: I am not sure whether I have understood what you are asking. Is it the title of the journal paper that you want to have in bold and italics, or the name of the journal itself? By first reading your question, I assumed the former, so the first part of my answer tackles that. If it's the latter that you're after, read the second part of my answer for an easier fix than what Guho suggests in his answer.


Typesetting the title in bold and italics

Quoting from the documentation of package apacite, on p.42 --- A coincidence? I don't think so... :-)

The following commands are currently implemented to format the reference list. If you want to customize them, you can study the source code in the file apacite.sty, copy it to you own package file, and adapt the code as desired.

(snip)

\APACrefatitle   Title (article style, default upright)
\APACrefbtitle   Title (book style, default italicized)

Therefore, if I understand correctly what you want to do, it suffices to add the following line in your code, after \usepackage{apacite}.

\renewcommand\APACrefatitle[2]{\textbf{\textit{#1}}}

Perhaps the advice to copy the source code of the package file was misleading; you probably do not want to do this for typesetting a single paper, but you'd consider it if this happens regularly. You don't need to touch the bibliography style (.bst), as the package provides easy customization for what you want to do.

Notice, however, that this changes only the style of the title of articles, therefore the first, unpublished reference to Ham et al. will not change.

result 1

If you want to also change that, you'll have to redefine the other macro too:

\renewcommand\APACrefbtitle[2]{\textbf{\textit{#1}}}

result 2


Typesetting the journal name in bold and italics

After \usepackage{apacite} you can add the following three lines:

\let\oldAPACjournalVolNumPages\APACjournalVolNumPages
\renewcommand{\APACjournalVolNumPages}[4]{%
  \oldAPACjournalVolNumPages{\textbf{#1}}{#2}{#3}{#4}}

This uses the existing definition of \APACjournalVolNumPages, instead of defining it anew, and just makes sure that the journal's name is bold (the existing definition will make sure to also use italics).

result 3