Sub Articulo 84.1
These parameters are reset by the size-changing commands \normalsize,
\small and \footnotesize. Unfortunately, they are set explicitly in the
definitions of those commands, so
a) you can declare your sizes after \begin{document} and anywhere
else where the font size has been set, like in floats. Since displayed
equations tend to only occur in the main text, you may be able to set
them once.
b) the "proper" solution is to make a .clo file with different
definitions of \normalsize, \small and \footnotesize, or a .sty file
that appends your settings to whatever the current definitions are:
\let\RegNormalsize\normalsize
\def\normalsize{\RegNormalsize
\abovedisplayskip\z@skip \abovedisplayshortskip\z@skip
\belowdisplayskip\z@skip \belowdisplayshortskip\z@skip
}