The idea is to introduce parameters in the "margin separator widget" 's configuration wich would allow margin separator to set custom margins (allowing to rescale the components in a section of  a pannels at will). This parameter's value would be signed, allowing to supress the current margin when negative, or to make the margin bigger when positive).
A second parameter would be the separator length, allowing users to use margin separators as (restricted-in-size) spacers if needed (making sure that everyone would notice the margin separator's presence to their liking)