# It seems to me that in principle I ought to be able to use the link
# script to substitute the necessary modules and then give the user an alternate
# command to invoke the revised system. Can someone please confirm whether this
# is possible and maybe flag some of the anticipated problems?
This is exactly correct. Copy the source code directories for the
module that need to be changed to any place on the system (your home dir).
First thing to do is change the Gmakefiles to reflect the name of a
different executable. For initial development this name is often of
an executable that will be installed in the source directory. Update,
modify, etc. When ready to unleash on the local user community, modify
the Gmakefile to install the executable in the appropriate GRASS location.
If the code is great, send it back to the entire user community!