Word VBA - Find a string and replace characters within that string.

[knifey]

Hi,
I'm trying to use a Word VBA find/replace to fill a word template table that is in an unusual format (MailMerge method dosn't work). I currently have a hard coded version working but when it runs the Excel data overwrites the formats of the table merge field.
Can anyone advise a way to do a Word VBA find for a string. Then replace characters within that string only (specifically find "<<" & mergeField & ">>" and replace "mergeField" only)?

Or maybe there is a better way to do this?

Any help or advice would be much appreciated.
Thanks,
Roy