Filter tikz node text through macro

Question

I would like to make a node style that "filters" the node's label (text) through a command, i.e. replace the node text with a macro, with the original node text passed as an argument to that macro. Specifically, in this case, I want to add a node \node {C} and have it typeset/draw \node {$\mathbb{C}$}.

I read the following answer: How can I pass the body of a TikZ node to a font-changing macro? and thought to do it like there, inserting $\mathbb\bgroup into the execute at begin node and \egroup$ into the execute at end node. This works (see MWE below), but I thought it would be better to use \ensuremath; also I might want to use \bm{\mathbb{C}} or \pmb{\mathbb{C}} for an 'extra-bold blackboard bold' symbol.

As soon as I add \ensuremath\bgroup or the extra \bm\bgroup, however, I get errors. Also if I define a separate macro \mymacro and use that in the tikzstyle definition, I get errors (see MWE below). Also when defining this macro somewhat differently (inspired by Use node text as argument for a macro) do I get errors.

Is there any way to achieve this?

\documentclass{article}
\usepackage{tikz}
\usepackage{amsfonts} %for the mathbb command
\usepackage{amsmath}

\tikzset{
  bb/.style={
    execute at begin node=$\mathbb\bgroup,
    execute at end node=\egroup$
  }
}

\tikzset{
  bb2/.style={
    execute at begin node=\ensuremath\bgroup\mathbb\bgroup,
    execute at end node=\egroup\egroup
  }
}

\def\mymacro#1{\ensuremath{\mathbb{#1}}}
\tikzset{
  my macro/.style={
    execute at begin node=\mymacro\bgroup,
    execute at end node=\egroup
  }
}

\def\mysecondmacro{\ensuremath\bgroup\mathbb\bgroup}
\def\endmysecondmacro{\egroup\egroup}
\tikzset{
  my secondmacro/.style={
    execute at begin node={\mysecondmacro},
    execute at end node={\endmysecondmacro}
  }
}

\begin{document}
  In text: \ensuremath{\mathbb{C}} %simply as text

  bb style: \tikz \node[bb] {C}; %produces the blackboard-bold C

  % Gives errors "Missing } inserted.", "\mathbb allowed only in math mode"
  % and "Extra }, or forgotten \endgroup."
  bb2 style: \tikz \node[bb2] {C}; %produces the blackboard-bold C

  % Gives errors "Missing } inserted" and "Extra }, or forotten \endgroup"
  my macro style: \tikz \node[my macro] {C};

  % Gives same error as bb2 style
  my second macro style: \tikz\node[my secondmacro] {C};

\end{document}

Answer 1

The latest version of PGF has a node contents=<node text> key which can be used in place of the {<node text>} in a node. It could be used like this:

\documentclass[tikz, border=5]{standalone}
\tikzset{node text/.style={node contents=\transformtext{#1}}}
\def\transformtext#1{\ttfamily(#1)}
\begin{document}
\begin{tikzpicture}
\foreach \l [count=\y] in {a,...,e}
  \node [draw] at (\y,\y) [node text=\l:\y];
\end{tikzpicture}
\end{document}