Hi, any implemented solution that went through standard testing, UAT, parallel runs and then go live should work without any interference when rolling over to the next year, as this has all been tested and signed off at that stage already (including rolling over to a new year). The standard configuration should include the copy of the closing balances to opening as well as copying net profit to retained earnings. This should happen as part of the workflow step, typically when the data is processed (Process step).
As part of an implementation it is good practice to document those kind of things, so I would encourage you to ask for this documentation as each implementation may vary, depending on the exact requirements.