I have just tried that and there is nowhere to input the code for the free version. I have 328 days remaining so I just tested it to see if MartinZ post was correct.

I was able to copy the Activation code but there is nowhere to copy it too. I even pasted it into the Insert activation code field (used for paid versions) and it split it over the three fields, but it didn’t extend the free registration period.

So it would appear there are limitations as to how far in advance you can re-register the free version. Perhaps this is like the old avast free re-registration only when you start to get notifications does the avastUI change to accept the free registration.