Default Value: If the variable value is not overridden at execution time, this value is inserted in the variable location in the path.
NOTE: When you edit an imported dataset, if a variable is renamed, a new variable is created using the new name. Any override values assigned under the old variable name for the dataset must be re-applied. Instances of the variable and override values used in other imported datasets remain unchanged.
Add Pattern Parameter
In the screen above, you can see an example of pattern-based parameterization. In this case, you are trying to parameterize the two digits after the value: