It is sometimes useful to have different modifier enabled or disabled for different passes. An alternative to using a different objects via visibility sets is to use the Before/After scripts to enable or disable the modifiers.

Modifiers can be accessed via MXS using either index (from the top), or by name - name is obviously more reliable since adding modifiers will mess up the index.

One way of getting an objects modifier by name is:

$'objectname'.modifiers[#modifiername]

(where 'objectname' is the name of the object and #modifiername is the modifier name - it pays to rename the modifier so you don't have multiples with the same name) and then

.enabled = true/false

You can of course also modify other properties.

*Note that the ' used either side of the object name is useful - it enables referencing objects with spaces in their names (not that I personally like spaces in names...)