This is an optional step. The original CSV circuit includes a trimpot. What it does in the circuit is sort of complicated, but here's what you need to know. Slight adjustments to the yellow plastic button on the trimpot affect the "ooomph" of the vibrato.

There are ways that you can leave the trimpot intact, and adjust it through the new housing. But since you're already replacing pots, it makes sense to replace the trimpot with a regular pot. Then, you can adjust that without opening up the casing. As before, pry away the metal tabs that hold the shell of the trimpot, and lift the guts off. The trimpot is not as robust as the regular pots, but the mechanism is generally the same.