what is the meaning of  “Never do anything by halves if you want to get away with it. Be outrageous. Go the whole hog.”  by Roald Dahl?

Applied to/by me it means if you're a thief, scallywag and revolutionary then fly your colours with pride, don't hide. I shouldn't be ashamed of the life I've chosen and should hope to get away with living as I do, a scoundrel in the eyes of the haves but hero in the eyes of the downtrodden. I encourage a life of rebellion, no shame upon my back lays for it belongs to the powerful. 

It simply means that if you want to do half of something, say eat half an apple or drink half a glass of water, get a pig to do it for you as they're good at that sort of thing. Avoid using cows, slugs and sheep to do half of anything as they're hopeless. Hope this helped.

I think he's saying to hide under the cover of audacity, that it will get people taken by surprise and they'll be stunned stupid hopefully for long enough to get away with whatever it is you're doing.