Hello,
I have experience with the Betfair API-NG, so I think I can help you out with the conversion.
How big is the application and which betfair api5 methods are you currently using?
The API-NG methods do not map completely to the api5 methods, so some changes and adjustments might be needed(different ways to parse data, different call structure etc.), but of course it all depends on the functionality that you are currently using.
If you give me some more details I will be able to evaluate the impact better.
Regards,
V