| Hi Burr, sorry I'm still not sure if I'm understanding... 
> But basically sliding the apex of the buldge around could be useful.
 
Do you mean a slider to control the bulge like this one here: ?
   
> And then the flip, I'm not sure how/if that works...I 
> understand it's about applying a curvature from the 
> existing surfaces, but then to be able to flip/invert that 
> could be some type of cavity tool. 
 
You can do this with the current Blend command by entering in a negative value for the bulge, that flips it to the opposite side, here's an example:
   
    - Michael |