Is it not that the lease you sign is for 3 years, and extensions are discretionary?
The mb did post huge losses last year and be keen to return to profitability. Maybe that is why they are changing the extensions.
But if you ask nicely, and give them valid reasons for the extensions, they may be favourable.
Bearing in mind they are quite helpful and reasonable. The limited choice for under 25,s is an issue.
You can only ask.