How to have a specific project setting editor only?

On my DefaultEngine.ini file I have the project setting r.PostProcessing.PropagateAlpha=0 however I want this value to be 1 when coding in the Editor (and back to 0 when packaging), at the same time I cannot set this value to 1 once the engine has booted as this configuration cannot be changed when the engine is already open apparently, I would appreciate any help on this.