TikZ pre- and append text/commands to all rectangle nodes

Question

Is there a way to pre- and append code (text and commands) to all nodes with the rectangle option?

I found this post which explains how to execute a command before every node, but this does not allow me to insert visible text, at least not when I tried it.

Edit:

\tikzset{
  ell/.style={
    % The shape:
    ellipse,
    %minimum width=6mm,
    minimum height=6mm,
    % The rest
    inner sep=0,
    draw=black,
    fill=white,
    font=\ttfamily},
  skip loop/.style={to path={-- ++(0,#1) -| (\tikztotarget)}}
}

{
  \tikzset{ell/.append style={text height=1.5ex,text depth=.25ex}}
}

\begin{tikzpicture}[
    >=latex,thick,
    /pgf/every decoration/.style={/tikz/sharp corners},
    line join=round,line cap=round,
    fuzzy/.style={decorate,
        decoration={random steps,segment length=0.5mm,amplitude=0.15pt}},
  ]

    \ttfamily
    \begin{scope}[start chain=1 going below,
            node distance=1mm,
            every node/.append style={on chain, scale=0.7,
                minimum width=5cm, align=center},
            every ell node/.append style={
                execute at begin node=(,
                execute at end node=)},
        scale=0.7,
        ]
        \node [ell] (stmt01) {2.  \verb|z = 20|};
    \end{scope}
\end{tikzpicture}

Answer 1

Welcome! Yes, it is.

\documentclass[tikz,border=3mm]{standalone}
\begin{document}
\begin{tikzpicture}[every rectangle node/.append style={
    execute at begin node=bla\space,
    execute at end node=\space pft}]
    \path node[rectangle] {hello} (0,-1) node[rectangle] {world};
\end{tikzpicture}
\end{document}

Since rectangle is the default,

 \path node {hello} (0,-1) node {world};

yields the same result.

UPDATE: As for your updated question, ell is not a shape but a style. So instead of every ell node/.append style= you need something like ell/.append style=.

\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{chains,shapes.geometric}
\begin{document}
\tikzset{
  ell/.style={
    % The shape:
    ellipse,
    %minimum width=6mm,
    minimum height=6mm,
    % The rest
    inner sep=0,
    draw=black,
    fill=white,
    font=\ttfamily},
  skip loop/.style={to path={-- ++(0,#1) -| (\tikztotarget)}}
}

  \tikzset{ell/.append style={text height=1.5ex,text depth=.25ex}}

\begin{tikzpicture}[
    >=latex,thick,
    /pgf/every decoration/.style={/tikz/sharp corners},
    line join=round,line cap=round,
    fuzzy/.style={decorate,
        decoration={random steps,segment length=0.5mm,amplitude=0.15pt}},
  ]


    \begin{scope}[start chain=1 going below,
            node distance=1mm,
            every node/.append style={on chain, scale=0.7,
                minimum width=5cm, align=center},
            ell/.append style={
                execute at begin node=(,
                execute at end node=)},
        scale=0.7,node font=\ttfamily
        ]
        \node [ell] (stmt01) {2.  \verb|z = 20|};
    \end{scope}
\end{tikzpicture}
\end{document}

Or you could append the stuff to each ellipse node with

\begin{scope}[start chain=1 going below,
        node distance=1mm,
        every node/.append style={on chain, scale=0.7,
            minimum width=5cm, align=center},
        every ellipse node/.append style={
            execute at begin node=(,
            execute at end node=)},
    scale=0.7,node font=\ttfamily
    ]
    \node [ell] (stmt01) {2.  \verb|z = 20|};
\end{scope}