You can keep adding hair to maintain or thicken your hairline. Why would it be foolish? His brand is his appearance. He's more popular and marketable then any bb since Arnold. It's not even close. 20M followers
From what I gather you might need a repeat if you continue to go bald farther back up your hairline and then they might have to do more transplants behind that front band that they did the first time. I hadn't heard of people needing repeat transplants in the same area they've already done unless they botched the first one. But I'm no expert.
