QGIS has a tool for creating multipart features in the Geometry Tools section. However, this is applied to a whole layer, which leads to the yellow selection in the image below when used (selecting the pentagon selects the stripes as well). I only want to join the three stripes, though. Right now I'm accomplishing this by saving the parts I want to join as a new layer, executing the tool and merging them back to the source layer. However this is quite tedious and unproductive. Is there a better way?