I want to write the prologue/epilogue in a book I'm writing in third-person narrative. I want my main story to take place before the prologue. Then when it finishes, the epilogue continues where the prologue left off. Can I write it my way?
The purpose of the prologue is to introduce us to the main story - it gives us the things we need to make sense of the main story. The prologue can absolutely be a space of time, or even a frozen moment in time that the main story will get us to.
The purpose of the epilogue is to tie up loose ends that the main story didn't address for whatever reason.
So yes, the prologue can absolutely be in the future (from the perspective of the main story) - it teases the reader to wonder how in the world the action of the story has gotten us here. The main story then would be about the unfolding of events that get us to the time frame of the prologue. And then the epilogue can then resolve any issues the main story didn't address.
For instance, I could write:
Prologue: Bob sat in jail, dejected, misunderstood. He wondered how he got here. He was a law abiding, average Joe.
Main Story: 33 years ago, Bob and Maximillian were identical twins. Separated at birth due to unfortunate yet hysterical clerical errors, Max went on to become a thief and Bob went on to become a nobody. And through another set of antics and twists, Bob gets caught up in a caper-gone-wrong and he ends up in prison.
Epilogue: Max confesses to the crime and Joe is set free.