Can I use my custom menus with RMS?

Yes.

If you prefer to use customized AutoCAD menus with
your copy of AutoCAD, you can add the contents of
the file RMSC.MNU to your menu file. This will enable
you to use your customized AutoCAD menus in conjunction
with BOSS RMS. For more information on customizing
AutoCAD menus, consult the AutoCAD Customization Manual
supplied with AutoCAD.

Once you have appended the supplied RMS custom menu
file to your customized AutoCAD menu, you need to
configure BOSS RMS to use this customized menu rather
than the default BOSS RMS menu. See the section titled
Menu Configuration in Chapter 3 for more information on
how to configure BOSS RMS to use a customized menu.