customizing index file name

[Shaw, James]

Does anyone know how to fix the .cfs file name in an index directory?
The deletable and segments file names are always the same, but we have
observed that the .cfs file name changes each time you index a content
directory with some changes to the directory (some deleted files, added
files, etc).  How is the name computed anyways?  Is there any way to fix
it?  Could there be other files generated in an index directory after
optimization besides these 3 files (.cfs, deletable, and segments)?