All customization, except for defining custom display functions and custom window commands, can be done through the customize interface:
Base set of character from which window IDs are constructed. This should be a
list of characters. By default, the home row (a s d f g h j k l) is
used.
Scope of all window operations. Used to determine on which frames to track
windows. A value of t means consider all windows on all frames, 0
(the number zero) means consider all windows on all visible and iconified
frames, visible means consider all windows on all visible frames and
current means consider only the currently selected frame. By default,
t is used.