If you are setting in/out points to import only a section of a video into your project then I'd say you are limited to one pair -- set them do the import and then set another.
If you are wanting to export several sections as one file there is no need to set in/out points. Magix editors (and it might help to know exactly which program you are using) are non-destructive. Simply delete anything unwanted, close the gaps and do your export. Your original files are unchanged.
Magix tracks are multi purpose. You can simply click drag from the media pool, a Windows explorer window, or a currently used track, to any track you like.