Missed this, but if you are still looking.. You need to change the ownership at the registered port. The number displayed on the boat has two letters before it. Those indicate the 'port d'attachée'. Then you need to get the appropriate licence to drive it. When you rent a boat, they don't require you have a license, but if you own it, you do.
I live near the Charente and it is not policed as it is a non commercial river. But most of the other canals are commercial and the rules need to be followed.
