1. A promoter swap method of genomic engineering to evolve a host cell to acquire a desired phenotype, comprising the steps of: a. providing a plurality of target genes endogenous to a base host cell, and a promoter ladder, wherein said promoter ladder comprises a plurality of promoters exhibiting different expression profiles in the base host cell; b. engineering the genome of the base host cell, to create an initial promoter swap host cell library comprising a plurality of individual host cells with a genetic variation found within each host cell of said plurality of host cells, wherein each genetic variation comprises one or more of the promoters from the promoter ladder operably linked to a target gene endogenous to the host cell; c. screening and selecting individual host cells of the initial promoter swap host cell library for the desired phenotype; d. providing a subsequent plurality of host cells that each comprise a combination of genetic variation, said genetic variation selected from the genetic variation present in at least two individual host cells screened in a preceding step, to thereby create a subsequent host cell library; e. screening and selecting individual host cells of the subsequent host cell library for the desired phenotype; and f. repeating steps d)-e) one or more times, until a resultant host cell has acquired the desired phenotype.