I've looked at some posts from a couple of years ago but couldn't find anything recent.

I'm using several MikroTik routers as PPPoE servers for ethernet connected retail clients at several sites. The routers are configured to use a central RADIUS server for authentication and accounting. To allow for offpeak downloads, I would like to reset the accounting session at 02:00 and 08:00 each day.

Is there any way to do this without terminating the actual PPP connection to the client? I really don't want to disconnect them twice a day. I don't have control over the client PPPoE routers so any solution needs to be initiated from the server side. I've tested cancelling the PPPoE active session and having the client router automatically reconnect but this terminates a running process on the client PC (I tested using wget).

I've also read that if you use PPPoE rather than hotspot then the router only accepts a subset of the Change of Authorization (/radius incoming) messages supported by MikroTik. Is this still true?

As far as I know PPP supports only disconnect messages, which means that client will be disconnected, in order to get new accounting/limitation options.