I argue regularly with people about the fact that it is a legal requirement to carry spare bulbs and fuses. Some people seem to think you don´t have to carry them but the risk is too high as the fine is prohibitive.
Technically if you read the French law it is only a requirement to have a replacement if a bulb has blown so if stopped by the police when all your bulbs are working you will not get a fine for not having them. (Unlike other items)
However if you are stopped because your break light/indicator etc is not working then as long as you have a replacement in the car then you will not get a fine.
The fine for having a faulty bulb is 80 euros so taking some bulbs makes a lot of sense to me.
You would just be required to change it ASAP, the fact is most of us are not capable of actually changing the bulb ourselves on modern cars and we end up getting a breakdown service or mechanic to change the bulb for us!
Having some spares is a big help in France in my opinion.