TL;DR
You should be able to copy/paste signals by shift-right and shift-left clicking them on any of those square fields where left-clicking it brings up a "Set the signal" or "Set the filter" dialog.What?
Signal/filter boxes have simple interactions: left click to set, right click to clear. They should also have shift-right click to copy, shift-left click to paste, precisely matching the gesture already usable on most entities in the game.Pasting into an incompatible entity/box will do nothing, just like the other "paste settings" operations, like how pasting a recipe from a chemical plant to an assembler does nothing.
Why?
How many of your combinators in 2.0 have multiple "Each" signals?How many of your train and platform schedules have repeated signals and numbers?
Adding logic and UI to copy entire conditions and outputs is tricky, but there's currently an unused shortcut that's perfect for copying signals around that players already know which would make complex combinators and repetitive schedules much faster to make!