"diff" and "patch".

You have created a program "prog.c", saved as this name and also copied
to  "prog.c.old". You post "prog.c" to users.  Next, you make changes
to prog.c

$ diff -c prog.c.old prog.c > prog.patch

Now, users can get the latest updates by running.

$ patch < prog.patch

By the way, you can make backups of your data easily.

$ cp /etc/fstab{,.bak}

Now, you do your edits to "/etc/fstab" and if you need
to go back to the original, you can find it at
"/etc/fstab.bak".