Do you want to use the contract generation functionality but have multiple contract versions? If yes, which is most probably the case then there are two approaches to template design of your contracts. One option is to have a template for every version type of a contract in which the merge fields cna be included. The second option is to use a functionality in microsoft word called if statements.
If statements help to insert/take out appropriate information based on a particular qualifier. For example, if it is a casual contract then XXX information will be removed.