Lead belongs to a different Lead Partition?

To allow purposeful duplicates, you first need to duplicate the lead and give it a new/unique email address (and store the real email address in a temp field).  Then once created, you would replace the email address with the temp email address.  This can all be done using a webhook and a single smart campaign.  To create that initial, unique email address, we use two tokens: {{lead.id}}-{{system.datetime}}

If you want something more permanent and more structural that what Dan suggest, you can also ask support to change the rules for automated duplicate detection. For instance, if Partitions A and B relate to 2 different Business Units, you can create a "Business Unit" field and ask support to set the duplicate detection to email + Business Unit.

Then, reprocess all leads from Partition A to "Business Unit" = "A", using a Change Data Value flow step in a batch campaign and the you will be able to import all you partition "B" leads with "B" in the Business Unit field.

You will also need some Lead Partition Assignment campaigns in your global workspace (the one that can access all partitions) to ensure proper assignment of leads and some automated data management smart campaigns in each workspace that automatically set the "Business Unit" field on lead creation when it's empty.

Another way to set this up is to ask support to set the dedupe rule to email + Partition.

All these need to be planned carefully, though, because it impacts structurally your database and the way you manage data.

Greg

Yet another method is to not use the UI-based List Upload and instead have someone build a simple web UI that uses the API's Bulk Import feature. When using the API you can dedupe on fields other than Email Address, so a whole list of new leads can be uploaded without fear (or hope!) of being merged.