% RequirePackage{atbegshi}AtBeginShipoutInit
documentclass{article}
usepackage{tikz}

usepackage{pgfkeys}
% Define the used keys in the following document
pgfkeys{
  /myKeys/.is family, /myKeys,
  default/.style =
  {
    width  = 1cm,
    my tikz commands={},
  },
  width/.estore in = kWidth,
  my tikz commands/.estore in = kTikzCommands
}

% This work, but is dirty
newcommand{myRectangle}[1][]{%
  pgfkeys{/myKeys, default, #1}%
  edeftest{noexpandnode [draw, minimum width=kWidth, inner sep=0pt, shape=rectangle, very thick, color=red, minimum height=1cm, kTikzCommands] at (current page.center) {};}
  begin{tikzpicture}[remember picture,overlay]%
    test %
  end{tikzpicture}%
}

% This does not work, and I'd like to make it work
newcommand{myRectangleB}[1][]{%
  pgfkeys{/myKeys, default, #1}%
  begin{tikzpicture}[remember picture,overlay]%
    node [draw, minimum width=kWidth, inner sep=0pt, shape=rectangle, very thick, color=red, minimum height=1cm, kTikzCommands] at (current page.center) {};
  end{tikzpicture}%
}


begin{document}

% Ok
myRectangle[width=10cm,my tikz commands={fill=blue, dashed}]
% No ok
myRectangleB[width=10cm,my tikz commands={fill=blue, dashed}]

end{document}

ERROR: Package pgfkeys Error: I do not know the key '/tikz/fill=blue, dashed' and I am going to ignore it. Perhaps you misspelled it.