Given a rewriting system G (its alphabet, the set of productions and the axiom) one can define the language of G by (i) taking out of all stings generated by G only those which are over a distinguished subalphabet of G, or (ii) translating the set of all strings generated by G by a fixed homomorphism. The "trade-offs" between these two mechanisms for defining languages are discussed for both, "parallel" rewriting systems from developmental systems hierarchy and "sequential" rewriting systems from the Chomsky hierarchy.
Ehrenfeucht, Andrzej and Rozenberg, Grzegorz, "Nonterminals Versus Homomorphisms in Defining Languages for Some Classes of Rewriting Systems ; CU-CS-027-73" (1973). Computer Science Technical Reports. 26.