as far as I know, you cannot execute the import/export of the user list if you aren't a workspace admin (don't think anaplan connect can).
However, what we do a lot is that a model has its own list of user (as a regular list). That list is used to set the roles & selective access and then exported to the user list of the model (that has to be done by a workspace admin). The non-workspace admin can then see the users, set the rights etc. They just need a workspace admin to effectively apply them.