No, it is not - LX recently published guidelines specifically advising agents that this is not allowed. They can't outlaw "back-to-back" ticketing completely, but there is no need to make it easy.

Your options are either to check in your bag for the entire journey (ZRH-VIE-ZRH-SIN) and risk a misconnect in VIE, or to store it landside in ZRH until you are back from VIE and then check it in for ZRH-SIN only.