In the following let Archive=/usr/local/src, or a similar path that refers to the location of the slisp sharable archive. Let Local=$HOME/src, or a similar path that refers to your personal copy of slisp in your home directory.
To aid in downloading a local version of slisp, a script called Scopy is located in Archive/slisp/bin. To run this script cd to the archive subdirectory in which the application you are interested in resides (e.g. Archive/slisp/sl), then run Scopy Local. The result will be that a directory hierarchy called Local/slisp will be created, and only those slisp modules required for the application will be copied. The basic application sl will always be copied, but the sl directory is very small.
This assumes Scopy is in your search path. It is useful in general to include Local/slisp/bin in your search path, (which will include Scopy once the initial download has been made) since the other configuration scripts reside there as well.
If Local/slisp already exists then files of the same name will be replaced from the archive copies. Thus, Scopy can be used to update your personal copy of Slisp after someone else has made changes. Of course it would be prudent to see what the changes are before you delete your own copies. This can be done on many machines by running diff -r Archive/slisp Local/Slisp, which will recursively list all the differences between the two directories.