The FetchXML statement is available in the data flow properties list. Follow these steps to set up an expression:

• Create a variable that can be loaded with the desired FetchXML statement. (Example: vFetchXMLModifiedOnDate)
• Right-click on the data flow canvas and select the Properties menu.
• Scroll down and find the properties in the group called Misc.
• Note the name of the property you want to modify dynamically at runtime. It will be named something like this:  [Dynamics CRM Source].[FetchXML]. This is the property containing the FetchXML statement.
• Scroll down and find the Expressions property. Set up an expression for the property noted above using a variable to modify it dynamically at runtime.  Here is an example of how that variable can be use in an expression to add the value from a variable: