Compared to the PsiCorp Penis, adding prims such as piercings to the vagina or tailhole is even simpler.

As first step, rez your vagina on the ground somewhere you can build. Then, position the prims you would like to add next to it, and before you link them, name them appropriately. The guideline for naming is simple, and explained here:

Firstly, the name line. It starts with the identifier for the current bit, so probably either "!vag" or "!tail", seperated by a comma, followed by the states you want this prim to be visible. So here´s an example of a piece visible in the aroused and gaping state:  

!vag, aroused, gape


Next, the description line. This part defines texture properties, incase you want your parts to use some of the default textures to blend in more. The first entry here defines which part type the prim should respond to for texture and color commands, so either flesh or fur. The second part tells the script which of the 4 available texture lists the prim gets its texture data from. Generally you dont need this last number unless you want to try and use default textures in your build somehow. A line could look like this: 

flesh, 4


After all the naming has been done, simply position the prims where you want them to end up, and link them to the vagina. This should be all, after a few seconds it should work as intended. If not, reset the vagina/tailhole script to force it to refresh its prim lists. Afterward, all prims will hide/show accordingly.