Did you ever needed a way to increase or decrease font size in xterm from script? I did... It took me quite some time to find out that xtermcontrol exists (which might be due to my use of rxvt instead of xterm for a long time).
Anyway, if you add following lines to your .bashrc:
alias f+='xtermcontrol --font=#+1' alias f-='xtermcontrol --font=#-1'...and you will be able to change font size in currently running xterm by f+ or f-.