> manufacture the chassis frame

Ship of Theseus notwithstanding, at that point, isn't it a new car if you're replacing the chassis?

Some manufacturers have a way of "officially" replacing the chassis, as in getting the chassis as a replacement part and procedure to replace it.

For example see BMW part number 51 71 7 409 410, chassis for F16 https://www.online-teile.com/bmw-ersatzteile/51717409410_Bod...

The law might look this or other way depending on where you are.