The spring-swap thing works like this:
There are Wicos with grommets inside, and there are Wicos with springs inside. If I remember correctly, he ones with springs inside have additional parts as well. So, youu could swap all the guts from a spring stick over into a grommet stick body, as the plastic shell and handle are the same either way. But you need all the parts to do it, so unless you've got a spring stick with a broken body, what's the point?
What you've probably seen Paige O talking about is replacing the spring that comes inside a spring-based Wico with a Happ Heavy-Duty spring from a p360, to give the stick a better feel.
Also, I though RayB said the grommet inside a Command Control stick was smaller than the one inside a regualr arcade Wico? Same inner diameter, of course, but different outer diameter. Maybe I'm mistaken here, though.
Edit: just checked out the post I was thinking of, and RayB says the grommet is the same, it's the leaf switches inside that are different. So nevermind.