“I gave a business in Los Angeles two post-dated checks for $200 in April for services to be rendered over a two-month period. They subsequently changed the dates on the checks and forged my initials in order to deposit them early. Can they be pursued from a civil or criminal standpoint?”
Possibly, but the important question here is: what are you hoping to accomplish? Did they render the service as promised? Are you looking to get your money back because they reneged, or you are unhappy with the service if they did render it? To pursue and win a civil action, you will need to prove that you were somehow injured by their action. If they are open to criminal prosecution, the state will prosecute them, and it is likely that you will get nothing out of it.
What they did was absolutely wrong; just be sure that you are clear what your own options are, and what the outcomes are likely to be.