Namespaces are sacred changing them could result in chicken sacrificing and other ungodly practices.
BizTalk is very xml-centric. If you change a namespace think about what references that schema, map, orchestration pipeline, rules composer vocabulary whose namespace you are about to change.
Best practice is to get namespaces right from the start. Look at the msdn’s best practice on standard namespace formats at the beginning of development. This prevents you from having hack a namespace change half way through development.
Sounds like common sense.
However!!!
A good BizTalker should be versioning their schemas via the namespace. Thus namespaces will have to change with new versions of your schemas. Be careful.