This is kind of a two part idea. The fist is having the ability to select and delete multiple sizes from the size section in the spec editor. You have to delete sizes one at a time currently and it resets your selection each time you delete which allows for errors if you are not careful.
The second part would be to give the ability to rearrange the sizes as it often happens where the size you add will automatically go to the bottom of the list so if you added a 4 to my current list it will show up under the 100 instead of being at the top. I understand why this happens and there is a workaround I use to fix it but it is very time consuming process that I am sure can be automated.