Add-in allows replacing Parts and Sub-Assemblies in an Active Assembly with one of the files currently opened in background, while also leaving as many constraints in place as possible. Add-in provides two separate buttons - Replace From Opened, and Replace All From Opened, which makes it easier to distinguish two functions; the user also has an ability to select more than one object to replace. Add-in opens a custom form with previews for all files opened in background for ease of navigation, as well as providing names when the cursor is hovering over the preview. Add-in has built-in protection from using files other than Part and Assembly, as well as from trying to replace an object with a currently active assembly, essentially creating recursion.