The below guidance deals with the situation where a landlord wishes to no longer retain a deposit under a scheme “during the tenancy”. This has nothing to do with when the tenancy has ended.
There is no provision within the Housing Act 2004 that once a deposit is protected under the Deposit Protection Service custodial scheme, allowing landlord to transfer it to one of the insurance schemes. This does not really matter because as the scheme is free there is no real financial loss. In addition, this makes sense because one of the penalties for failing to protect a deposit is that a landlord can be told by the court to protect the deposit using the custodial scheme. If there were provision to move the deposit out during the tenancy, then a landlord could easily avoid the punishment by protecting the deposit then removing it a few days later!
Insurance based scheme
The landlord can easily un-protect a deposit from either of the insurance schemes during the tenancy and then re-protect the deposit with another scheme of his choosing (either the other insurance scheme or the custodial scheme).