Go into /home/user/.icewm or /etc/X11/icewm and find the “keys” file, it should say
key “Alt+Ctrl+t” xterm (or something similar like x-terminal-emulator)
change this to
key “Alt+Ctrl+t” konsole
Now, whenever you press Ctrl-alt-t konsole will come up instead of xterminal
You can play around with the other things in there too.