Once I land in Germany, what would the procedure be?
Is the train to Poland within the airport or do they let you leave the airport as part of your transit?
Flight to Berlin, train from Berlin to Warsaw. The station's not in the airport; you'll need to get a bus, subway or cab. I usually use subway or uber however the bus goes straight to the station. You have to buy the ticket (a couple of dollars) from the machine at the airport door where the buses stop.
As far as I can tell from reading the German government websites (these may change), Covid restrictions say you can leave the airport for transit providing you spend the minimum time in Germany, and it's a good idea to have an onward ticket booked.
Thinking about it, you may as well get a connecting flight from Berlin Tegel to Warsaw. Because both Germany and Poland are in Schengen, there aren't (normally) any immigration controls to go through, and they aren't even allowed to stop you (they just check ID). Whether there's any Covid checks right now, I'm not sure. Worth checking with Lufthansa (whose customer service is unfortunately a bit annoying).
Any rumors on what changes are coming February 28?
Everything was supposed to be relaxed a bit, however because the infection rate is rising here and they've confirmed that the new mutations are here already, it's anybody's guess. They may get tougher at the borders; I personally hope not.
I'm lucky because I can wait until then before buying my ticket. I'll be travelling to the UK via Germany or Holland on Lufthansa or KLM. I'll need to get a Covid test immediately before flying (you'll probably have to as well). Warsaw Airport do a speedy service, however there are plenty of places in town, and as far as I can tell, the day before is OK.
There are various pages on Facebook for expats in Poland and specific ones for expats in Warsaw. If you use facebook, it might be worth joining those pages since people are discussing travel and borders on them all the time.
pages on Facebook
I had a quick look at one for Americans in Warsaw and they were saying that they aren't letting people from there into the Schengen zone at all. That was a post from 3 days ago. I don't know how accurate that is, however it's worth having a look and see what people are saying.
I'd strongly recommend contacting the border guard via the address on this page: strazgraniczna.pl/pl/kontakt/1946,Komenda-Glowna-Strazy-Granicznej.html