Most of the features that you will want to customize can be set
with resources in your .Xdefaults file. However, key
bindings, mouse button bindings, and menu definitions for mwm are
specified in the supplementary .mwmrc file, which is
referenced by resources in the .Xdefaults file.
If you do not have a .mwmrc file in your home
directory, you can copy it as follows:
cp /usr/lib/X11/system.mwmrc .mwmrc
If you do not have a .Xdefaults file in your home
directory, you can create one with any text editor. Once you have
these files in your home directory, you can set resource values in
them as you wish. Because the .mwmrc file overrides the
system-wide effects of the system.mwmrc file, your
specifications will not interfere with the specifications of other
users.