not clobbering installed xdm config files in make install?

[Matthieu Herrb]

Hi,

I'm looking for a way to get automake to do what the old imake 
Install*NoClobber() rules did, in particular for app/xdm/config, as it's 
  annoying to get your customized xdm configuration overwritten 
everytime you install a new xdm.

Any idea if automake has such a feature, or how to add it without 
loosing other benefits of automake?

Thanks.
-- 
Matthieu Herrb