Make a recursive copy of your source tree before any changes (pristine version). E.g., copy project/ to project-pristine/.

After the changes, run this command:

$ diff -crN old new > output.diff
- or -
$ diff -crN project-pristine project > name_of_change.diff

On the target system in /path/to/project/../:

$ patch -p0 --dry-run < ./name_of_change.diff

Remove --dry-run to make it take effect.