Nice work TBH. I am not certain about the 'Earthlike' appearance, however. According to Wikipedia:
"Neptune is similar in composition to Uranus, and both have compositions which differ from those of the larger gas giants, Jupiter and Saturn. Neptune's atmosphere, while similar to Jupiter's and Saturn's in that it is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen, contains a higher proportion of "ices" such as water, ammonia and methane. Astronomers sometimes categorize Uranus and Neptune as "ice giants" in order to emphasize these distinctions.[13] The interior of Neptune, like that of Uranus, is primarily composed of ices and rock.[14] Traces of methane in the outermost regions in part account for the planet's blue appearance"
..which leads me to think that a warm Neptune would probably have an appearance like Jupiter or Saturn, as the icy compounds would melt to a gaseous state and the trace methane would most likely have blown away in the Solar wind. Also, with a Neptunian day being only a bit over 16 hours, there would probably be no distinct 'impact site' indicating the side facing the Sun when the nova hit, most likely the 'damage' would be spread around the equator reasonably evenly (Neptune's axial tilt is roughly the same as Earth's).
In my minds eye, I see the post-cataclysm Neptune being a sick yellow/orange colour, perhaps with a blueish tinge at the poles, with massive and violent storms through the equatorial regions as previously-frozen gasses well up from the boiling interior. There might also be a gaseous 'tail' streaming away into Neptune's dark side, much like a comet's, as the outer layers are stripped away by the solar radiation.
Having said all that, who knows what would happen to the outer planets if the Sun went Nova, it's all speculation really. Importantly for the Transneptune plotline however, the Solar System becomes uninhabitable post-cataclysm, and I am just concerned that this Neptune looks too pretty! You've done a great job on preparing the surface texture, really nice work.
