xprop man page, XPROP(1) manual page
The xprop utility is for displaying window and font properties in an X server. One window or font is selected using the command line arguments or possibly in the case of a window, by clicking on the desired window. A list of properties is then given, possibly with formatting information.
set property-name
This program can set the X11 window icon for any given window, to that of a given image file.
usage: xseticon [options] path/to/icon.png
options:
-name : apply icon to the window of the name supplied
-id : apply icon to the window id supplied
Sets the window icon to the specified .png image. The image
is loaded from the file at runtime and sent to the X server;
thereafter the file does not need to exist, and can be
deleted/renamed/modified without the X server or window
manager noticing.
If no window selection option is specified, the window can
be interactively selected using the cursor.[xdotool man page)
xdotool lets you programmatically (or manually) simulate keyboard input and mouse activity, move and resize windows, etc.