Mixing fare codes on a return flight

What are the limits on mixing fare codes when booking a return flight. I know you can mix cabin classes. But do they have to be at the same level of flexibility. E.g. can I book, say, an S-class PE outbound leg (in order to upgrade cheaply to UC with miles) and then the cheapest economy fare code on the return leg. This could be especially useful on long east/west routes where one way is overnight and the other is daytime. I expect there are some restrictions with this in the system but wondered if anyone had any experience. Everyone wants UC for overnight surely, but lower classes easily ok for daytime flights.
Cheers,
p.

[Neil]

Yes you can. You can combine any fare codes as long as there is availability.

Neil

agree you can do this although I have encountered staff (even on the gold line) that say you cannot - probably because some of them seem to know very little about anything other than booking a simple ticket.
I have not found a way to book this online though so I think you will need to call them. On line always tries to give you the same code each way.

[Neil]

You can book different fare codes online by using this page on the VS site, although that is limited to certain fare codes only.

[mitchja]

Yes this can be done but always remember that when you combine mixed fare codes, the lowest fare rules apply to the whole journey.

Thanks for these useful replies.

Neil, esp for that link to booking page with selected fare codes, which is v useful. Also v useful, mitchja, to know that the lowest fare code rules apply for the whole flight. I wouldn't have assumed that and would prob have fallen foul of it before long.

Ta!