How to replace multiple products in existing subscriptions with a new product, adjust quantities accordingly, and retain grandfathered pricing?
You can use the Bulk Product Swap tool in Bold Subscriptions to replace existing products in subscriptions with a new product and set a quantity. The new and existing products should be in the same subscription group.
Please note that the Bulk Product Swap tool doesn’t retain grandfathered pricing, however, you can use the Bulk Product Pricing tool to assign the same pricing to the new product.
More details on using bulk updates in Bold Subscriptions can be found here - https://support.boldcommerce.com/hc/en-us/articles/17574024850452-Bulk-Updates-Overview.