I am surprise that you were able to get a 2019 M3 LR RWD?
I was thinking that the LR RWD was discontinued in 2018, and was replaced by the Mid Range RWD, and then by the SR/SR+ RWD?
Note: I understand your change of heart but on the first year, expect a 15% depreciation, also you will have to pay another 9.5% sale taxes.
Other alternative would be to put some white seat covers.
Painting could be changed with film cover.
AWD is great, but not as really needed in California, unless you quite often go to ski in the Sierra.
Why not wait for a litte bit, and make a reservatuion for a Model Y White/white AWD FSD.