Rigid targets are free to translate and/or rotate according to the modifications you have made. However, they are not to change shape at all: hence the name "rigid".

1. Click the Transformer Rig icon to open the toolbox.
2. Click the Transformer Rig tool. You are prompted to

   Select geometry. [Accept Targets] to add selected geometry as Targets of Transformer Rig.
   

3. Pick the surfaces to be modified.
4. Click Accept Targets. The selected surfaces become flexible targets.
5. You are prompted to:

   Press [Free] and [Pre-Defined] to add modifiers!
   

6. Choose the tool (either Free or Predefined) and select the geometry to serve as modifiers, then click Accept Modifiers.

   You are prompted to

   Press [Flexible] and [Rigid] to add geometry to transform, [Free] and [Pre-Defined] to add modifier geometry, [Constraints] to add constraint geometry, and [Go].
   

7. Click the Add Rigid Targets icon.
8. Pick the surfaces that should change position or orientation, but not change shape.
9. Click Accept Targets after selecting appropriate surfaces.
10. The rigid targets are now highlighted green, with the word Rigid on top of them. You can modify the attributes of the target by clicking it with the to open this menu:
    

    This menu enables you to switch a target from rigid to flexible, and vice-versa. You can also prevent rotation of the target by choosing Rigid Translate, or constrain it further by choosing one translation axis.

11. Now add Constraints if they are required. Click the AddConstraints icon.
12. Picking the appropriate geometry.
13. Click Accept Constraints to add the geometry as constraints.
14. Click Go to finish
15. Choose Pick > Object to leave the Transformer Rig toolbox, and select the modifier surfaces.
16. Choose Transform > Move to reposition the modifier surfaces.

    Notice the rest of the surfaces are modified accordingly. Specifically, notice that the rigid target surfaces retain their shape.

    Bonus movie: Commit and Revert.