Hello Helge,
It is already possible in current Metashape release version. To keep the current asset and generate a new one of the same type you should click on the asset's label in the chunk's contents of the Workspace pane, uncheck "Set as default" option and then start the generation of the asset of the same type.
This applies to depth maps, dense point clouds, mesh models, tiled models, DEMs and orthomosaics.