yes they can do rolling call ups.
i think if they sign Johnson/ Power to contracts and they play this year, they may send down Samuelson or/and Fitzgerald which then opens some other call ups.
They also would like Rochester to make the playoffs. if they were safely 8n or eliminated you might see rotating call ups.
They've already used three of the four free roster recalls. Sending people down doesn't make those slots available again, it's not a token system.