Is it possible to take a ring like this one and make the shank wider, without melting it down and re-making the ring? Also, is it possible to plate 14kt yellow gold to make it look more like 18 kt yellow gold?
Plating works pretty well (yellow on yellow), but I can't see how to make this wider. Unless you would consider using stacked bands next to it. Some are as narrow as 1.5mm, so one would not add allot to the ring - just enough. On the other hand... wedding bands sometimes get soldered to rings, so this could be done, I suppose.
Something like THIS (restricted link to photo, 1.5mm yellow gold with yellow diamonds, $700). An all white version of the ring is listed as well for $600 or so. There are many other sources, of course. Some tiny rings like these are listed by www.EstateDiamondJewelry.com.
What could look very nice would be a pair of white (or yellow) gold bands (with or without grain set diamonds in the same style) that sit or are soldered either side.
The best look is if those bands are not flat but 'triangular' in cross section, so the slope awat from the existing center part.