changing system definitions

[rpg@cs.brown.edu]

Can anyone tell me what happens to previous versions of systems when I
mung the sysdcl.lisp file for it?  My problem is that I want to alter
a system by adding and deleting files from its declaration.  But I
want to keep the old version around till I'm sure it works.  Is this a
reasonable thing to do?  Do I have to keep the old sysdcl.lisp in
place? (keeping old source files in place is a problem for us because
we're short of lispm file space)

Thanks,

Robert