For transduction, you would be dependent upon mutualist virii. The problem is how much control can be exerted over those virii that seek out and assimilate new genomes. Other than that, it wouldn't be too much different from mutation, just with a bit more restrain upon it. The real problem here is, fluff-wise, this strategy calls for intelligent critters with clouds of virii flying about them all the time, picking and choosing what DNA is to be assimilated by the host. They would almost always be sick, too.
Conjugation isn't much of a problem on a macro-scale. It's just that big organisms tend to favor stability over flexibility, but fuck it, this is fantasy, right? So, the important thing is that physical contact of a living cell to viable genetic material is needed. from there, the cells behind conjugate, and the cells behind that conjugate, and so on. The problem is the homeobox gene complex would have to be squirrely and self-correcting, otherwise you'd get weird freaky shit. So, all it would take is a handshake if the conjugator was strong about it, or sharing a kiss or a blood-brothers type ritual if not.