Version:            (using KDE 4.1.1)
OS:                Linux
Installed from:    Compiled From Sources

When creating a custom keyboard layout, one would create a new file instead of modifying an existing file, so there are no collisions.

The keyboard layout module of kde normally reads out the file /usr/share/X11/xkb/rules/base.xml (maybe the .lst, too?), as far as I know.
To add my own keyboard layout, I would like to add a new rules file, together with a new symbols file and I would like to be able to switch to those using kde's layout switching functionality.
The problem is, that kde only reads the base* files, but ignores everything else.
My suggestion is to make it (optionally) selectable which rules files should be read to get a list of available keyboard layouts.
That would make it possible to integrate custom keyboard layouts way better.