I can't quite understand what your trying to achieve. I assume it's to slice an image for a web page such that there's no visible joins. Is that correct?
If you want to do that it's quite simple in XaraX. The image on this web page is of a XaraX image in 4 slices. I have attached one image, to show that it is 1 of 4 sections
The page is here: web page
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