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A user can use the program "patch" to take a diff file and
apply it. Also, read the man page (or search google) and you
will find that you can patch against a particular date, like
if you want to patch only against the last release code version.

From "man patch"

patch takes a patch file patchfile containing a difference
listing produced by the diff program and applies those
differences to one or more original files, producing
patched versions.