Can I replace a 4 wire ballast with a 5 wire one?
The new ballast has an extra blue wire.
My understanding is that yes, you can. The 5 wire is simply a newer, safer design for a ballast. However, should you? Unless you are working on one ballast in a large system, it may be wiser to upgrade to LED technology and solder/cone new fixtures into your workspace, then you'll never have to deal with those darn ballasts again!
Useful Diagram: http://www.electrical101.com/ballast-diagrams.html
Tutorial: https://www.youtube.com/watch?v=CeRkLdrMwqQ (Unsure as to how accurate this may be, there are other online resources as well)
Disclaimer I am not an electrician nor do I pretend to be one. I do a fair amount of DIY projects and home improvement but am not a professional!