Quick update after talking to TAP. Just in case this is useful for others.

Even though not explicitely mentioned in fare rules, TAP allows routing changes + date changes. After reading this in another forum I prepared 2-3 itineraries and called TAP, ready to suck up the fare difference for a different routing way out in 2022.

The experience with their phone service has been actually "okish". Yes, there has been a wait (50m), yes the first person had no authority whatsoever (what is YQ?), but after being re-routed to the reservation department the person there has been ok. She precisely answered cancellation costs (200 EUR each direction, no YC) and when suggesting the date + route changes things went quick and smooth.

What surprised me a bit is that the surcharge I had to pay was exactly the difference between the ticket price of the new flight minus the ticket price of the old ticket. I have seen that being handled way more arbitrary by other airlines. Also, I was surprised that they allowed a date change that is +1y after the original ticket purchase.

All in all pretty happy about the outcome and how TAP handled it TBH.