Teach Soap

I've been looking at some making pics of cupcake and cake soaps, and have some questions, if anyone can answer them. Some of the cake soaps in particular, have top and sides 'frosted' or iced in amazing patterns. To me , this means that the cake soap has been mDe and then unmoulded, and frosted, or iced. But I thought that soap that has set up enough to be unmoulded, couldn't have frosting added because it wouldn't stick. Is this right? Can anyone tell me how it is done? The same principle applies to cake slices that appear to have been made with a base, then filling, then another half of the cake stuck on top. How can they be stuck together?

Thought I'd reply to this myself in case anyone else is interested - I watched some youtube videos and I think I've got it now - piping will work, apparently, on just-unmoulded soap, but not cured soap. makes sense......