You have numerous options. For example, you could create:
1. a set of custom Quick Parts for each option and insert them as required;
2. a dropdown formfield or content control from which to choose the contract type, then have that selection trigger either the updating of fields or bookmarks in the document with the variable content;
3. a separate template for each contract type, then simply choose whichever one you want to base a given contract on. This is by far the simplest approach.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]