If my security deposit check doesn't clear, can my landlord come into the house and change the locks?

That would be a no.

While you are in breach of the lease agreement, a landlord is not entitled to use self help. ?You have to be given a three day notice. ?I suppose the landlord could argue that there never was a binding agreement as you never put down the security deposit [why are you trying to skirt the truth you gave him a bum check], but i think a court would still say you have to be given a three day notice followed by an unlawful detainer, which case you will lose. ?Depending on your state laws, you may be entitled to damages for an unlawful eviction, but once the landlord follows the law and gets an unlawful detainer judgment, it will harm your credit rating and make most future landlords refuse to rent to you. ?It might be better to work out a compromise with the landlord as to a date when you have to move out in return for no formal eviction.