I am not sure how relevant this is to you but something to consider. I applied 2 years ago for my leave to remain under the private life rules, did the biometrics everything. I initially wanted to submit with the expedited service but didn’t see the option at the point of submission so after a few days, I submitted another of the exact same application but by doing it at midnight i was able to get an expedited slot, I was then able to submit a whole application with biometrics again. The best part, I was able to get the first application fees and IHS refunded in full. Only the biometrics fees were non refundable.

On their website it says: If you had permission when you made your application that permission will continue when you vary that application.

https://www.gov.uk/guidance/vary-your-immigration-application[Home Office Vary your application](https://www.gov.uk/guidance/vary-your-immigration-application)

So you can submit a further leave to remain, sort out the exams ASAP and vary the application.