I'm pretty sure there must be molecules or signaling pathways that upregulate specific enzymes but yeah as you say, epigenetically via specifically made peptide

I'm pretty sure there must be molecules or signaling pathways that upregulate specific enzymes but yeah as you say, epigenetically via specifically made peptides or genetically via mRNA injections, one could increase the quantity of a specific ensyme, the easyness being a product of how well delineated and specific are the genes/allele responsible for its encoding. The medicinal applications are endless, e.g. increasing FAAH ensymes for next-gen sleep enhancers, or increasing specific ratios of phosphodiesterases for next-gen mood stabilisers/antypsychotics/anticonvulsants/antiepilleptics. It seems like a very underfunded generic target.