You can do it with a Workflow SDK Script

You can use CSV or Excel as your source, but for my example, I pushed it into a SQL table.

Then I created a simple Workflow

My Custom Query is:

SELECT [id]
      ,[UserName]
      ,[UserPassword]
      ,[LFGroup]
      ,[IsReadOnly]
  FROM [LFExternalTables].[dbo].[LFUsers];

And my SDK Script looks like this:

        Protected Overrides Sub Execute()
            'Write your code here. The BoundEntryInfo property will access the entry, RASession will get the Repository Access session
            Try
                Dim ui As UserInfo = New UserInfo()
                ui.Session = RASession
                ui.IsDisabled = False
                ui.CanUsePassword = True
                ui.CanChangePassword = False
                ui.Name = GetTokenValue("ForEachRow_UserName")
                ui.Password = GetTokenValue("ForEachRow_UserPassword")
                Dim sGroupName As String = GetTokenValue("ForEachRow_LFGroup")
                If Not String.IsNullOrEmpty(sGroupName) Then
                    ui.JoinGroup(sGroupName)
                End If
                Dim sIsReadOnly As String = GetTokenValue("ForEachRow_IsReadOnly")
                If sIsReadOnly.ToLower() = "true" Then
                    ui.ReadonlyAccess = True
                Else
                    ui.ReadonlyAccess = False
                End If
                ui.Save()
            Catch ex As Exception
                WorkflowApi .TrackError(ex.Message)
            End Try
        End Sub

You may want to add code to the SDK Script to check if the user name already exists, but this is the basics.