How to make a size slider (not length but scale size).
Load the nif in outfit Studio and right click and scale shape (then move the object back to the correct location with the item size reduced).
Next go to sliders and choose "Set Base Shape".
Now with the model smaller, right click and export as object.
Close and restart Outfit Studio.
Load the CBBE reference, Load your nif as an outfit (Do a Conform to all under the sliders function at the top).
Create a new slider (Name it Cock Size or something).
Highlight your mesh, Set slider to edit mode and go to the top and click slider - import data - import from obj (load the object you made earler).
With the slider at 100 the cock mesh will be smaller and with the slider at 0 the cock mesh will be bigger (you can invert this by setting the slider to 100 by default and where it says invert = true in the osp... yeah you'ld have to edit the osp for that).
Optional Mask off the Cock so the balls are the only thing unmasked on your mesh and create a Zap Slider (this optin when check in bodyslide will remove the balls).
Save project as (include the cbbe shape name it do all the other fun stuff and now you have a fully customizable cbbe body with an adjustable cock and removable balls...
It really is that simple.
Hmm looks like you have 2 meshes, one for cock and one for balls... would need to scale both (which means you might want to extend the cock to the body and have the ball mesh completely removed with the zap slider... just a thought)..