Is there a way to customize the xschem user interface, and if so what skills should I have to do that.

you can add new menu commands to xschem and add new toolbar buttons. Any xschem action can be triggered bu these new menu/button widgets. You can create a tcl script for example

myscript.tcl

and add this to your xschemrc:

lappend tcl_files myscript.tcl

so it will be loaded automatically when xschem starts. Otherwise you can load the script with

source myscript.tcl

Atached two simple tcl files, one adds a new menu entry, the other adds a new toolbar button. There are many xschem specific commands, these begin with the xschem keyword. Examples:

xschem netlist

xschem simulate

xschem load schematic_file.sch

All these commands are documented here.