You can customize the standard agreement actions and override their default behaviour. The following agreement actions can be customized by using the code mentioned in their respective Visualforce pages:
Action Name
Description
create_new_agreement
Create New agreement
create_offline_agreement
Create Offline Agreement
create_oppty_agreement
Create Agreement From Opportunity
create_child_agreement
Create New Child Agreement
store_executed_agreement
Store Executed Agreement
clone_agreement
Clone Agreement
amend_agreement
Amend Agreement
renew_agreement
Renew Agreement
Customization is achieved by using the exisiting Visualforce page containing javascript code and configuring the action to invoke the javascript code in a new Visualforce page before displaying the agreement to the user for editing. Ajax javascript libraries supplied by Salesforce are available for use in the javascript code.