Map your objects to a different texture in your render layer by right-clicking the Image Name attribute on a file node to create an override.
This feature is most useful if you want to apply a different texture on each layer to a set of objects.
In this example, the couches are assigned to a lambert, which is mapped to a greyish texture. To assign the couches to a plaid texture instead, you can do as follows:
A file node subcollection is created, as well as a corresponding file texture name override.
Enable or disable the file node override to switch between the two textures.