Add Deformer node in control rig is by default stacking because most use cases assume the mesh wants to use the default linear blend skin deformer before applying multiple lattice deformer rigs on top of it. However it does offer an option to override the default deformer if you prefer, which you can enable by changing the execution phase setting on the Add Deformer control rig Node from “After default deformer” to “Override default deformer”. This should allow the deformer in the second instance of the same rig to override the deformer in the first instance. You might need to make some minor adjustments to the deformer to include both linear blend skin as well as the lattice deformer since in this case the default linear blend skin deformer would be overridden as well.
Btw, it is worth mentioning that if you plan to integrate deformers into character rigs instead of using deformers as ad-hoc shot sculpting tools, you can take a look at this EDC thread https://forums.unrealengine.com/t/is-there-a-way-to-bake-deformer-graph-animations-in-level-sequencer-into-an-animation-sequence/2298398/11, where it shows that you can use auxiliary deformer bones and Post process AnimBP to make the rig work better with animation baking tools and potentially other sequencer features
Hope this helps! Happy to go into more details as well.
Jack