The easiest way to do it is to fire you and switch to contract-based employment. I know lots of people working for multinational companies headquartered in Germany and everyone based outside Germany (EU, US, Ukraine, Russia, Brazil, you name it) are on "freelancer"/"consultant" contracts (working full time, some people have been working like that for more than a decade)
Well, it was similar to opening a bank account - first they ask for a WP, then dig through their internal instructions which don’t mention TE, and then you get “mai dai”
It doesn’t matter if there’s a regional office or not. It’s a separate entity, period. As long as you’re not paid through that regional office, you’re fine
if you're required to do 365-day reports (which is an automatic thing as you have to go to the immigration for an extension anyway) instead of 90-day ones, that's definitely means "exempt from 90-day reporting"