Agree absolutely with Rob and Ostarella. One should always do a little research on an agent you’re querying to see if she’s in the market for your manuscript, and there’s nothing wrong with tailoring your query letter a bit to fit her preferences. But tailoring your manuscript to an agent’s tastes? It’s not uncommon to query 30-50 agents. So one should write 30-50 versions of a novel manuscript? That’s one of the most ludicrous suggestions I’ve ever heard.