[jsmith45]

It is not in general legal to change prefixes and reserialize an XML document. Some official XML formats including XML Schema allow attribute values to reference prefixes in xs:QName types. One needs to bind the schema to detect that.

But it gets worth with XSLT using the prefixes in XPath expressions in attributes. If the prefixes are changed those values also need to be updated to change the prefix too, which requires complete knowledge of the format. This is because one cannot programmatically detect something like attributes that use custom data types that reference the prefixes in scope, but XSLT's xpath expressions show that W3C considers it legal to create such custom formats.