Redefining a letter to itself

An \expandafter before \active tokenizes the following \def without the changed category code of e:

  {
    \catcode`e=\expandafter\active
    \def e{\char`e}
    SomeText
  }

Another trick works via \lowercase. The definition is done with the active ~ that is changed via \lowercase to e. Afterwords the category code is changed.

  {
    \begingroup
      \lccode`~=`e %
    \lowercase{\endgroup
      \def~%
    }{\char`e}%
    \catcode`e=\active
    SomeText
  }

\documentclass{article}
\begin{document}
% Now I can't use e, so I have to use something else instead. 
% I tried ^^65, but it doesn't work (65 is ASCII hex value for e)
  {\let\z\def
    \catcode`e=\active
    \ze{\char`\e}
    SomeText
  }

or


  {\let\z\edef
    \catcode`e=\active
    \ze{\stringe}
    SomeText
  }
\end{document}

Exploit a benign effect of the “missing space syndrome“:

{\catcode`e=13\def e{-\char`\e-}Test}Test\bye

With an abstraction:

\def\defactive#1#2{%
  \begingroup
  \lccode`~=`#1\lowercase{\endgroup\def~}{#2}%
  \catcode`#1=\active
}

{\defactive{e}{-e-}Test}Test

\bye