Two Approaches:
Use existing \Diamond of amssymb
\documentclass{article}
\usepackage{stackengine,amssymb,graphicx}
\newcommand\DDiamond{\ensurestackMath{%
\stackengine{.5pt}{\Diamond}{\scalebox{.75}[1]{$-$}}{O}{c}{F}{F}{L}}}
\begin{document}
$\DDiamond$ as created\par
$\Diamond$ is the amssymb version
\end{document}

If you want the cross-line to be a "dash" with space around it, reduce the value of .75 in the \scalebox to, for example, .6:

IMPORT JUST ONE MnSymbol
Import just \DDiamond from MnSymbol. Thus, it does not screw up the other definitions of amssymb. I've declared it as \mathrel but you can change that.
I've set up convenient macros (between the %%%% delimiters) for importing stuff from MnSymbol. Once those macros are set up (copied/pasted into your preamble), the import goes as follows:
\ImportFromMnSymbol{C}
\DeclareMnSymbol{\DDiamond}{\mathrel}{C}{120}
%\MnSymbolGlyphs{C}
\MnSymbolGlyphs{} shows the font table for MnSymbolA, B, C, etc, given the subset as the argument. This is how to locate a glyph's subset and slot number.
\ImportFromMnSymbol{} sets up for importing symbols from the specified MnSymbol subset.
\DeclareMnSymbol{<macroname>}{<math category>}{<subset>}{<slot>} to grab the MnSymbol from the specified slot in the given subset.
\documentclass{article}
\usepackage{amssymb}
%%%%
\def\MnSymbolGlyphs#1{% IF ONE NEEDS TO LOCATE GLYPHS
\usepackage{MnSymbol,fonttable}%
\AtBeginDocument{\fonttable{MnSymbol#110}}%
}
\def\ImportFromMnSymbol#1{%
\DeclareFontFamily{U} {MnSymbol#1}{}
\DeclareFontShape{U}{MnSymbol#1}{m}{n}{
<-6> MnSymbol#15
<6-7> MnSymbol#16
<7-8> MnSymbol#17
<8-9> MnSymbol#18
<9-10> MnSymbol#19
<10-12> MnSymbol#110
<12-> MnSymbol#112}{}
\DeclareFontShape{U}{MnSymbol#1}{b}{n}{
<-6> MnSymbol#1-Bold5
<6-7> MnSymbol#1-Bold6
<7-8> MnSymbol#1-Bold7
<8-9> MnSymbol#1-Bold8
<9-10> MnSymbol#1-Bold9
<10-12> MnSymbol#1-Bold10
<12-> MnSymbol#1-Bold12}{}
\DeclareSymbolFont{MnSy#1} {U} {MnSymbol#1}{m}{n}
}
\newcommand\DeclareMnSymbol[4]{\DeclareMathSymbol{#1}{#2}{MnSy#3}{#4}}
%%%%
\ImportFromMnSymbol{C}
\DeclareMnSymbol{\DDiamond}{\mathrel}{C}{120}
%\MnSymbolGlyphs{C}
\begin{document}
$\DDiamond$ as imported from MnSymbol\par
$A \DDiamond B\quad\scriptstyle A \DDiamond B\quad\scriptscriptstyle A \DDiamond B$
$\Diamond$ is still the amssymb version
\end{document}

\documentclass{...}and ending with\end{document}. – albert Sep 13 '18 at 10:25