Confessions of an Automationeer, Part 206: Two Approaches to Restomodding
In the Automationverse, there are two ways to restomod a car: either by cloning the base model and engine family (and by extension, their respective trim and variant) simultaneously, or by merely cloning the trim of the original base model. In general, the donor car should be at least 20-30 years old compared to the restomodded trim. So here's a brief rundown of both methods, and how they should be compared.
Above: By clicking on the Clone All button (second row, first from right) in the Car Designer after selecting a specific trim, and then setting the new car's base model year 20-30 years further forward, you can create a remanufactured restomod from your donor car.
The first (and most comprehensive) approach is called
remanufacturing, in which you clone the entire car's base model and engine family, thereby creating a new car trim and engine variant in the process - there's a dedicated button for it in the car designer (second row, first from the right). Using the donor car for
ARM34 (which I'd hosted) as an example, I remanufactured it with new materials for the chassis and engine, enlarging the latter in the process while also fitting a more extrovert aero kit (along with modernized light clusters) to suit the updated aesthetic. Inside, the interior was upgraded with lighter, higher-quality materials and a modern infotainment system, while uprated brakes, suspension, and tires help it harness its increased output more easily.

Above: The original '92 Morrison Kestrel (left) compared to its remanufactured restomodded version, the Kestrel RM (right), created by clicking on the Clone All button in the car designer and setting the car model/engine variant years 20-30 years later than those of the donor car. In-game, the two are different base models from different model years.
Refurbishment is another option, but compared to remanufacturing, it's not quite as extreme. You simply clone a trim of the donor car, then set that trim's year to 20-30 years after the model year. You do, however, have the option of replacing the original engine with a new one whose family year matches that of the new trim year.
Above: A sneak preview of a refurbished (rather than remanufactured) restomod which I am planning to submit for a different forum challenge. Both trims share the same base model year and use the same body/chassis materials, suspension types, and engine placement. However, the restomod utilizes a completely new engine instead of a new trim of the original engine. Please note that neither the restomod nor the donor car are 100% visually representative of the finished product.
The resulting restomod retains the same chassis materials, engine placement, and suspension types as the base model, but can still be retrofitted with more advanced technology (infotainment, suspension components, safety equipment, driving aids, etc.) much like a fully remanufactured restomod.

Above: Another way to create a restomod is to clone the selected trim, set the new trim's year 20-30 years further forward, and install more advanced technology (including a new engine whose family year matches the new trim year) as you see fit.
In short, both restomodding methods have their merits; while refurbishment preserves and retains the chassis and bodywork configuration of the donor car (thus maintaining some semblance of originality), remanufacturing, though more expensive, allows for free reign as to which body/chassis materials, engine placement/orientation, and suspension types can be used for the restomod. But whatever approach you pick, no expense should be spared, and to that end, a heavy investment in positive quality points across various areas is generally recommended.