How can I ensure that a new hard drive is not viewed as a new machine by Mac App Store?

I'm about to take my iMac (running Mavericks) in to the Apple Store for a precautionary hard drive replacement (at Apple's request; they identified a batch of faulty Fusion drives and mine is one of them). What steps can I take in preparation to ensure:

1. That the Mac App Store recognises my identity after the drive replacement, to avoid the problem that this chap is having, and
2. (Assuming no problems with [1] above), that the new hard drive is not identified by the Mac App Store as being a new machine, since this would effectively rob me of one of my 5 permitted installs. The MAS does not seem to have a '(de)authorise this computer' option in the same way that iTunes does. Is MAS authorisation controlled by the machine's iTunes authorisation? (same question applies to iBooks, in fact—though that app does have its own ‘authorise this computer’ menu item, making matters still more confusing).

Or, am I worrying unnecessarily?

Any advice gratefully received.