Tri-X was changed to remove a number of heavy metal ingredients that were harmful to the environment. The heavy metals were replaced by organic compunds that served the same purpose. Actually, one of the chemicals removed was an organo-metallic ingredient.
D-76 is D-76 but with a different packaging method used to allow a single package mix. Sequestrant is also added to prevent scum and cloudiness.
My scratch mixes and the prepackaged version react identically towards all of the films I have tested them with.