When selecting an image for portrait or bodies, instead of loading all of the images at once, it only loads them as they become visible in the window.
This makes the manual selection actually possible with large portrait collections. The dialog will still take a while to load initially, and performing searches or locking to race can still be slow, but it's better than before, or can actually work if before you didn't have enough memory.
Note: Incompatible with versions of Improved Random Portraits before 1.0. If you do use it with them, I think it'll work as long as you have this mod later in the order, otherwise improved random portraits will wipe out this mod's changes.
Edit: Link briefly had zip that was named right, but had random portrait mod contents instead.