xschem reads system installed xschemrc (in your case ~/share/xschem/xschemrc) and after that it reads the xschemrc in the directory where xschem has been started if any, otherwise it reads from ~/.xschem/xschemrc if any. Do not change ~/share/xschem/xschemrc since it is all comments and does nothing. If you want to work on sky130 create an empty directory, copy the ~/.xschem/xschem_library/xschem_sky130/xschemrc into it and start xschem from there, and edit this xschemrc if you need to change something. If you want to work on madvlsi i think you should create a directory, copy ~/madvlsi_git/madvlsi/xschemrc into it and start xschem from there. Again change this xschemrc if you need to. Refer to bminch docs for details.