A document has a Hyperlinks collection, of all the Hyperlink objects in the
document. A Hyperlink object has an Address property and a Subaddress
property. The Address is the portion to the left of the # and the Subaddress
is the portion to the right. A link to another location in the same document
will have a blank Address. A link to the start of another document will have
a blank Subaddress.

You can both read and write the Address property of a Hyperlink object. So
what you need to do is cycle through the Hyperlinks using a For Each-Next
loop, read the address, change it as necessary and write it back. Write some
code that does that on a single document. Then put the code into the inner
loop of the macro shown in article below in order to make a batch process of
it, replacing the find/replace code that is already there.

Find & ReplaceAll on a batch of documents in the same folder
http://www.word.mvps.org/FAQs/MacrosVBA/BatchFR.htm