I have seen the ability to swap components and instances but I have not seen the feature to replace a regular grouped or non-grouped object with a component/instance that already exists.
For example, you have a design that was brought in from a new person or the library was not active when created. That item has multiple buttons that are inconsistent and off brand. My desire would be to replace the current grouped button by right-clicking on the group and replacing with the correct button component/instance from my existing library.
I am used to Sketch and it has the functionality to replace any item with a component. Is this currently possible or is it in the roadmap for functionality?