Generally speaking, the process would begin with obtaining something called a "certificate of conformance" from the dealer/manufacturer, then to change the headlights to ones for a left hand drive version, take the car to a garage in France to have the equivalent of an MOT, present all the paperwork to the appropriate Préfecture, pay the fee and come away with a new registration number. We have done this before with cars and motorcycles and know how it works.
Our trusted UK garage person told us that the replacement headlights would be expensive and he could not get hold of them. We would have to get them in France and a French garage would have to fit them. When we looked into it further it seems that changing them is no easy task and, according to Mazda, the French garage would have to get in touch with Mazda technical support and be "talked through" the process as it would involve reprogramming the car's electrics.
Alarm bells started ringing when we discovered this! You can see how it could all go wrong, that it could cost a fortune and we could end up being without a car at all for weeks if it didn't go right first time. Not to mention that messing with a modern car's electrics is rarely a good idea! Just to be sure, I emailed the Mazda main dealership that's nearest to us in France and they said they could not do the work.
We have decided that a good solution is to sell the Mazda in the UK and buy a French car instead, using the ancient and rattly old Peugeot to get us to France in the short term. As I write this we have the car up for sale in one of those online auctions you see advertised on TV so we are on tenterhooks to hear if it sells. We're not prepared to let it go too cheap but........what to do if it doesn't sell?
We could leave it in the UK for use when one or other of us returns and take the old and rattly Peugeot to France instead - that one would migrate more easily (and cheaply). That's not an ideal solution; having your best car stood doing nothing for most of the year while we rattle round in a scruffy old jalopy does not make sense.
We could trade it in for a different good car that would migrate more easily - one with headlights that switch to left hand drive! Time is running out to get that organised. **
We could take it to France and use it there for a few months, returning to the UK with it sooner than we thought we would, and stay here until we've changed it. Although are we allowed to do this - to turn up at the border with a visa that leads to French residency and a car that we are not importing?
Questions, questions, and the answers can be hard to find!
Well, one way or another we will find a solution and I expect this is only the first of many "challenges" that will crop up as we go through the migration process!
**This option is not really an option. Further research tells us that if we import a car that we have owned for less than six months we will have a hefty bill for the VAT and duty. The only viable option therefore is to use the proceeds from the Mazda to buy a French car.