This Custom word addin
It will replace Keys marked with @[KeyName] with a value specified by a windows form. Note that you can add defualt values with =. Eg @[KeyName=Defualt Value for Key]
Simply add variables or keys to replace by typing @[KeyName] or @[KeyName=WithOptionalDefaultValue] into word doc and open the windows form using the button from the custom addin's ribbon's Button. Then fill in the values to replace and then hit replace.
writen in more or less 3 days including commenting and testing.