So my question is as in the title
I wanna know if i have to (write down) my tablet area in osu lazer or does it save in my settings?
Also if ill switch tablets will that effect enyrhing if the tablet is smaller/larger or the area and the way it feels will be the same.
Thanks in advance.

I mean you could try it. just make sure to write the tablet settings before hand. what i think is that settings dont get saved in and only get saved on the computer. And i think that if you switch to a bigger tablet the area will feel slower than the smaller tablet. I am not sure but you could try.

Configuration is saved locally, on your computer.

If you switch tablets, as long as your tablet area is the same then it should feel similar enough. Other factors such as latency, hardware smoothing, pen weight, tablet surface, etc. may have an effect on overall feel however.