No. The Cumulus number linked to your Migros Login is automatically linked to your Migros Online account. If you want to change the card, go to "My Cumulus" in your account and click on the "To my Cumulus account" button. You will then be automatically transferred to the Migros customer portal, where you can unlink your Cumulus card and add another one.
After switching from your LeShop.ch login to the Migros Login, your Cumulus card may not be linked to the Migros Login. In this case, you must link your Migros Login to the Cumulus card.