Are you in the right place? All you have is a SXEmacs source tarball and you don’t have git installed.
Yes? OK, great, read on.
You will have the toughest time of it I’m afraid because you will have to do everything manually. But it isn’t too bad. No worse than for any other project.
Your hacking cycle will look something like this:
diff -urNp pristine-tree working-tree > my-sxemacs.diff
A note of caution here: Please ensure that you are diff’ing clean
trees. In other words, run
make distclean in your working tree
before creating the diff.