You might not get a 4.7 to a 4.4 but it all depends on the athlete. A good athletic trainer can work to get the fast twitch muscle fibers working efficiently and work with the muscle memory and stretching and you can improve statistical speed. You get muscles to work at peak performance and lengthened out by stretching you can improve most players coming out of High school in my opinion.
You can't train the "it" but you can give a athlete better tools to use when they "have it".
Here is one study that looked at someones loss after a decreasing training:
http://www.ncbi.nlm.nih.gov/pubmed/1...ubmed_RVDocSum
Here is another in the conclusion states: Complex training can be another valuable method for short-term power and speed improvements in athletes in isolation or in conjunction with other power development methods.
http://www.ncbi.nlm.nih.gov/pubmed/1...ubmed_RVDocSum
Just my .02