It is very unwise to change lawyers in the middle of a lawsuit. Allen Stanford, the Houston investment counselor who has been charged with fraud, has changed lawyers a couple of times already and is seeking to change lawyers yet again. His case is criminal, but the same principle applies: a lawyer or a set of lawyers understand nuances about a case that cannot be simply interchanged. When a lawyer deposes a witness, for example, the lawyer acquires valuable information about a witness’ ability to testify. These observations include much more than just what the witness says in response to a particular question. When a client changes lawyers, much of those observations are lost.
Change a lawyer if you must, but be very sure when you do so. It now looks like Mr. Stanford had differences with his lawyers about trial "strategy." It better be important strategy to incur the risk of losing so much "institutional" knowledge.