There have been many times while working on my project that I've wanted to replace every instance of an object, either on one specific layout, or every layout in my current project.
I'm unaware if there's currently a way to do this, but I think it would be great if I could right click on an object, then select either "all instances in layout" or "all instances in project" which is pretty self explanatory.
Additional functionality would be to replace all objects selected, which could be done with either another function in the right click menu, or an additional field in the object properties itself which lists the object name, but is editable (either drop down, text, or both.) This way you can select the object, and change the field in the object properties and voila! All selected instances are replaced.