You can change the font configuration by modifying fonttext.cfg and fontmath.cfg, see Configuration Options for LaTeX 2e. You can find this document with
texdoc cfgguide
Hovever, it is not recommended to change the font setup. Here is a quote from fontdef.dtx:
% \section{Customization}
%
% You are not allowed to change this source file! If you want to
% change the default encodings and/or the font shape groups preloaded
% you should should create a copy of \texttt{fonttext.ltx}
% under the name \texttt{fonttext.cfg} and change this copy. If
% \LaTeXe{} finds a file of this name it will use it, otherwise it
% uses the standard file which is \texttt{fontdef.ltx}.
%
% If you don't plan to use Computer Modern much or at all, it might
% (!) be a good idea to make your own \texttt{fonttext.cfg}. Look at
% the comments below (docstrip module `text') to see what should
% should go into such a file.
%
% To change the math font setup use a copy of \texttt{fontmath.ltx}
% under the name \texttt{fontmath.cfg} and change this copy. However,
% dealing with this interface is even more a job for an expert than
% changing the text font setup --- in short, we don't encourage either.