Hey, sorry that I missed this for one day. As for your questions:
First, there's a box you need to check first before the tool lets you click on the button to load a custom slope shape. There should be an example included in the download but basically, black is the ground/slope, white is air above.
Second, if I understand what you want correctly, the tool cannot do that. The custom tile can only do "top down"-style slopes, because calculating the angle of a non-standard slope is not trivial.
However, the tool is able to do wrap-around circle slopes, they're the right-most slopes. If you want an upside down version of it, just rotate the slope by 180°. If the ground doesn't let you do that, then rotate the input by 180° and make another tile set with the tool, that should give you the upside down version of the inner half circle slope. If you don't quite get what I mean, I could run it for you if you give me your inputs.
