All objects in DISE can be merged together to form a single object. This is a convenient way to position and move an unlimited number of objects at once. By default, some properties will not be applied to merged objects, such as shadow and transparency - selecting the object, these features are grayed out in the Object Properties.
Creating a single object
Select the objects you want to merge, and either right-click or click the Group button in the toolbar and select Merge as single object.
You can at any time select Split into objects to revert back to the original objects.