\documentclass[]{article}

% PROBLEM
% \(re)newcommand gets overwritten for Accents \< and \>:

\newcommand{\<}{\emph{first definition of <-accent}}
\renewcommand{\>}{\emph{early redefinition of >-accent}}

% WORKAROUNDS

% save original definition and overwrite later
\let\MyLessThanSaved\<

% define as TextDefault (can be done before or after loading fontenc):
\DeclareTextCommandDefault{\>}{\emph{TextDefault of >-accent}}


\usepackage{lmodern}
\usepackage[LGR,T1]{fontenc}
\usepackage{textalpha}
% font encoding switch declarations:
\newcommand{\LGR}{\fontencoding{LGR}\selectfont}
\newcommand{\Latin}{\fontencoding{\encodingdefault}\selectfont}


% RESTORING
% restoring as "normal" macro results in problems in Greek text
% \renewcommand{\<}{\MyLessThanSaved}
% restore as "TextCommandDefault" (for all font encodings except LGR):
\DeclareTextCommandDefault{\<}{\MyLessThanSaved}


\begin{document}

\section*{Test accent macro name clashes}

The LGR font encoding defined until version 0.12 from 2014-12-12 the
\verb+\<+ and \verb+\>+ shortcuts for Greek dasia and psili accents as
``TextAccent'' macros (see fntguide.pdf).

This definition moved to ``textalpha.sty'' wich also
makes LGR the default encoding for these accents.

This means that with \verb+\usepackage{textalpha}+, the accent macros
are undefined in all other font encodings and can be given another definition.
However, due to the internal working of \verb+\DeclareTextAccent+, earlier
definitions of these macros are overwritten.

Test: macro defined before fontenc loading: \<

Test: macro (re)defined after fontenc loading: \>a

Test: accent macro kept in LGR: \LGR \<h \Latin

Test: accent macro overwritten also in LGR: \LGR \>h \Latin

Test: TextCommandDefault at end of group: \texttt{\<}

Test: Tab accent kludge: \a<

\section*{LGR Transkription und Makros}

\LGR  'a  `a  "u  <a  >a \\
     \'a \`a \"u \<a \>a \~a

\end{document}
