Why are end users creating list members and why are these list members not coming from a Data Hub or a trusted source system? When you have users creating these list members, you are losing the audit trail, data governance, as well as creating an action for the users to run which can lead to concurrency issues.
So, before we start trying to figure out a solution for you, what are trying to accomplish and why?
This might be a longer solution than you anticipate and has one additional step. I will try to mention it stepwise:
By default identify who is running the import and isolate one import action from another
Create a fake user list with all the mail ids present
Create a new module (M1) dimensioned by native User list and create 4 line items - import?, User List (formatted to fake user list), Write Access and Flush. This module will isolate users basis a boolean that they select before running the action. You will add a write access on Import? basis the write access line item. Attaching the blueprint here:
Create an action that imports the flush line item into the import? line item. we call this 'Action 2'
Create the module (M2) you are using to do the import and dimension it by the fake user list. We will filter this module basis the selection made by the end user in step 2. Attaching the blueprint here:
Create a saved view in the module created in step 3 by filtering basis the Filter line item
Create one action to import into the list with the saved view as source. we call this 'Action 1'
Create a process with Action 1 and 2
Create a new DB and publish 3 items - M2 with the required line items and users in the page, M1 with only import? line item and users in the page and the process
The step to import would then be
add your items to the grid with code and name (M1 view)
Check the import boolean. This basically makes the boolean inactive for other users till the action in the next step is run
Run the action. The second action removes any selection done in Import? line item thus the boolean is again active for all users.