Here in the US it is no longer legal to use those "warranty void" stickers that have to be broken to open a device. So we can open ours. I'm not sure if that's the case in the Czech Republic. If you don't have any stickers then you can freely upgrade. If you do have stickers then you need to check with your local laws to see if that is legal.
Also, you should keep any parts that you upgrade and revert to stock before sending in for any warranty work. This is because if they need to replace some or all of your machine you don't want to lose the parts you upgraded.
No idea what modules they use. You'll have to check when you get it.
A bus station is where a bus stops. A train station is where a train stops. On my desk, I have a work station…