Mod editing on the fly

Is there a setting that mod devs can use that can use new changes in game?
For example a mod that changes build speed, Change it so that it take longer and we can see the effect in game and for comparison to the original speed

You want to use the "Allow Mod Data Updates" cheat that Uber provides. If enabled, press Ctrl+Alt+P and it will reload your mods.

Thanks

Your example requires a server mod, in which case liquius is correct. Client mods merely need a UI refresh (F5 by default), and you may be able to get away with less