Adding characters with similar font to an existing Handwriting environment

Question

I'm using the Handwriting environment presented in this question enter link description here, however, I'm not getting on how the code sets all the variables in the environment to be written the same way. To explain, I'm using \mu and \alpha in my answers but they don't look the same as the rest of the characters in the answer, .

The code:

\usepackage[no-math]{fontspec}
\usepackage{amsmath}
 \newfontfamily\Chalkduster[NFSSFamily=Chalkduster]{Chalkduster}
\usepackage[subdued, defaultmathsizes]{mathastext}
\MTfamily{Chalkduster}
\Mathastext[Chalkduster]

\newenvironment{Handwriting}{\MTversion{Chalkduster}\MTdonotfixfonts
  % adjust some additional glyphs
  \Umathchardef\prod 1 \symmtoperatorfont `∏\relax % mathop
  \Umathchardef\sum  1 \symmtoperatorfont `∑\relax % mathop
%  \Umathchardef\in   3 \symmtoperatorfont `∈\relax % not in CHALKDUSTER?
  \Umathchardef\int  1 \symmtoperatorfont `∫\relax % mathop
  \Umathchardef\neq  3 \symmtoperatorfont `≠\relax % mathrel
%
% This syntax works with luatex not with xelatex
  % \Umathcodenum`∏=\prod
  % \Umathcodenum`∑=\sum
  % \Umathcodenum`∫=\int
  % \Umathcodenum`≠=\neq
% So we repeat
  \Umathcode`∏ = 1 \symmtoperatorfont `∏\relax % mathop
  \Umathcode`∑ = 1 \symmtoperatorfont `∑\relax % mathop
  \Umathcode`∫ = 1 \symmtoperatorfont `∫\relax % mathop
  \Umathcode`≠ = 3 \symmtoperatorfont `≠\relax % mathrel
}{\par}