Menu position for skin modifier resizing (Ctrl + A) Ctrl + A allows you to resize vertices with skin modifiers applied.
You can also search for skin resize in f3.
But I didn't find this feature in the top menu.

Do you know the menu location for this feature?
As far as I know there isn't, but you can access the x and y sizes from the Tool panel > Transform > Radius X/Y. You have to be in edit mode, in vertex select mode and you have to select at least one vertex. 

You can't use the proportional editing that way though.