For the time being, collection type assets are defaulted to linking, whilst object type asset are defaulted to appending. For now there’s no way changing this defaulted behavir. Linked assets in a project will update when you reopen the scene or you reload it in outline>blender file.
Please take a look at my proposal, it meets all your needs and brings much more useful functionality. https://devtalk.blender.org/t/variation-system-my-proposal-based-on-current-asset-browser