Niiice, he gobbled them right up! (And I like how he climbed that tree to come in from above; looked like he was trying to air assassinate those mice, pfft.) If you're going to make the mice-to-rats switch soon, my advice is to save a couple of the mouse fuzzies, in case you need to rub the rats with mouse scent in order to persuade Gargamel to give them a try at first. Another option is feeding a combo of 1 mouse + 1 rat, where you give the mouse first, and then follow up with the rat as the "chaser" while your snake is still in food mode. Lastly, if the frozen/thawed mice don't have a strong enough scent to transfer well onto the rat, you can ask a nearby reptile store (if you have one) for some of the used bedding for their feeder mice, and put the rat in a plastic bag with the bedding to make it more strongly mouse-scented.
There's a chance that Gargamel will give you an easy time and just make the switch without even needing any of the above techniques, but it's always good to be prepared.