The 16-year-old drove a Peugeot 208 T16 on last weekend's Rally di Roma Capitale, which looks likely to be his last outing in the car before he switches to a Fiesta R5 for next month's Rally Liepaja in Latvia.
Rovanperä will turn 17 on October 1 and a day later will take his practical driving test in Finland, having already passed the theory test last week.
He has already tested a Fiesta R5 car at M-Sport's Greystoke base and will drive the WRC2-spec car before contesting Rally GB, and again on the Monday before heading to Australia for November's Coffs Harbour-based WRC finale.
M-Sport managing director Malcolm Wilson said he was excited to see how Rovanperä would adapt.
"He's about the same as Jari-Matti [Latvala] was when he first came," said Wilson, "and there's always something really exciting about seeing these young guys progress.
"Having him with us for GB and Australia is fantastic news - he's going to be a real talking point on the last two rounds of this year's world championship."
While the son of one-time world rally winner Harri Rovanperä is no stranger to R5 cars, his only competitive outing in an M-Sport car was at the wheel of a Fiesta RS WRC, which he drove to second place on last year's Bettega Memorial Rallysprint.
Wilson and Rovanperä's manager Timo Jouhki confirmed no deal had been agreed beyond the end of this season.
Rovanperä has been shortlisted for Hyundai's young driver programme next season and Jouhki wants to see the outcome of that shootout first.
"It's tough [the selection process for the Hyundai seat], there are a lot of good drivers in there and it's really difficult to predict which way this will go," said Jouhki.
"I would say the second option for us would be to stay with Malcolm."
"We already talked about next year with him and we have a long history of working well together and good relations, so this could make sense."
Jouhki confirmed the thrust of Rovanperä's 2018 programme will be six rounds of the world championship in Mexico, Argentina, Finland, Spain, Britain and Australia.
Doubt has been cast over any extended British Rally Championship commitment, however, owing to potential date clashes.
Jouhki added: "We wanted to do the BRC, but this is becoming more difficult now because of the clashes with two of the rallies - we are contemplating this right now.
"Kalle doing a championship isn't so important, we are interested in the experience from these events. We will look at the asphalt [BRC] rounds.
"And, of course, Rally GB is a round of BRC as well."