Just checking, because I do not think it is possible in Construct yet. However, the current game I am working on uses too much memory for mobile. A simple solution is to replace the current sprites with lower resolution ones. However, Construct does not keep the original's relative scale, and scales it down.
It would be great to have an option that we could replace assets with lower or higher resolution versions, and all the instances in our project would update without changing the relative scale.
For example, suppose I change a sprite to a 50% version. Construct would then automatically calculate that all instances used are relatively scaled up by that value, no matter their actual size in the layout.