How to perform a \global\renewenvironment

Create a dummy (or alternate) environment in the global scope (preamble), here, XEnvironment, and then in the \DisableMyEnvironment macro, globally reassign by way of

\global\let\MyEnvironment\XEnvironment%
\global\let\endMyEnvironment\endXEnvironment%

MWE:

\documentclass{article}
\usepackage{xcolor}
\newenvironment{XEnvironment}[1][]{}{}%
\newenvironment{MyEnvironment}[1][blue]{%
    \begingroup
        \color{#1}%
}{%
    \endgroup
}%

\newcommand*{\DisableMyEnvironment}{%
    %% How make this global??
    \global\let\MyEnvironment\XEnvironment%
    \global\let\endMyEnvironment\endXEnvironment%
}%

\newcommand*{\MyTestText}[1]{%
    Some before text

    \begin{MyEnvironment}
        This should be in #1.
    \end{MyEnvironment}

    Some after text%
}

\begin{document}

\MyTestText{blue}

%\DisableMyEnvironment% <-- This works, but want it to work when used in a group as follows
\begingroup
    \DisableMyEnvironment
\endgroup

\medskip\par
\MyTestText{black}


\end{document}

Edit: First approach didn't seem to work with optional arguments.

Edit 2: Found an easier way using \globaldefs:

Final answer:

In spirit of answering how to do a \renewenvironment global:

\documentclass{article}
\begin{document}
  \newenvironment{test}{HELLO}{WORLD}
  \bgroup
    \globaldefs=1
    \renewenvironment{test}[1][world]{foo #1}{bar}
  \egroup
  \begin{test}[hello]
  \end{test}
\end{document}

Second answer:

Two commands loosely inspired by \makeatletter and \makeatother: \makerenewglobal and \makerenewlocal. When \makerenewglobal is called, \renewenvironment do only global definitions. If \makerenewlocal is called, it does the oposite: makes all \renewenvironment-definitions local.

\documentclass{article}
\makeatletter
\let\@local@newenv\@newenv
\long\def\@global@newenv#1#2#3#4{%
  \@ifundefined{#1}{\global\expandafter\let\csname#1\expandafter\endcsname\csname end#1\endcsname}{\relax}
  {\let\def\gdef\expandafter\new@command\csname #1\endcsname#2{#3}}%
  \l@ngrel@x\expandafter\gdef\csname end#1\endcsname{#4}%
}
\gdef\makerenewglobal{\global\let\@newenv\@global@newenv}
\gdef\makerenewlocal{\global\let\@newenv\@local@newenv}
\begin{document}
  \newenvironment{test}{HELLO}{WORLD}
  \bgroup\makerenewglobal
    \renewenvironment{test}[1][world]{foo #1}{bar}
  \egroup
  \begin{test}[hello]
  \end{test}
\end{document}

First answer:

In spirit of semi-generality; a command, \makeenvglobal{theenv}, that makes a environment global:

\documentclass{article}
\gdef\makeenvglobal#1{%
  \global\expandafter\expandafter\let\csname #1\expandafter\endcsname\csname #1\endcsname
  \global\expandafter\expandafter\let\csname end#1\expandafter\endcsname\csname end#1\endcsname
}
\begin{document}
  \newenvironment{test}{HELLO}{WORLD}
  \bgroup
    \renewenvironment{test}{foo}{bar}
    \makeenvglobal{test}
  \egroup
  \begin{test}
  \end{test}
\end{document}

prints foo bar