Change of tenancy required

Tenancy Types and Management

We have a house (previously our main home)rented out to four sharers, all professional working people. The current mortgage provider permits us to rent out this property on the existing repayment mortgage. However, it will not allow us to renew this 'permission to let' arrangement as we have informed them that the current tenants all rent on separate room-only tenancies. It looks like that this is the only reservation the provider has so we should be able to change the tenancy to an AST in four people's names.

Is this feasible? Is there a specific procedure? We would prefer not to change the mortgage as its terms are favourable.