I think with the Boost update everything including data rollover stays the same, I recently had my phone plan updated & I’ve not noticed any difference or change
There is a bunch of info (and FAQ's) regarding the system/plan update at this link :
I think the main things you will need to do, is re-setup any autorecharge (payment info doesn't carry across), and download/setup the new Boost app.
* I am a Boost Australia customer. This is a peer to peer community where users help each other.