Yes, if you upload your list via Salesforce, when you update your list in SFDC, it will automatically sync in ListenLoop.
If you upload your list via CSV, you can simply turn/off accounts to control your campaign.
You can always upload more accounts at any time. Please note, for data integrity purposes, there's no "delete" of accounts after they've been added.
Feel free to contact us if you need anything via firstname.lastname@example.org or Online Chat.