As it isn't that bad quality, it should be be able to copy-resized an icon to its next neighbor, i.e. 32x32px to 16x16px and/or 48x48px.
This means, a user could copy a icon from 16x16 -> 32x32 -> 48x48 -> 64x64 -> 128x128 or vice versa.
Generally, it's no good idea to resize a 16px image to 128px, but the user himself is responsible for the graphics quality, so .paf assistant won't stop him to do this.
Now, images can be copied to their next neighbor in the correct size.