UV Deluxe provides similar functionality to the modo script you mentioned. It's just a script and doesn't depend on any plugins. Set your map size at the top, then set your density in the box that says "Pixels per cm" (under the Ratio rollout) and then select the UV shells you want to scale and hit the "Set Ratio" button.
Hi, I don't know if this was answered already, I've searched the forum for this and some results came up, but I wanted to know if there is a way to do this without plugins. After I unwrap a piece I need to set every Island to a 256 pixel resolution. So I need something like this…