Can I get an excess on a day return

[tannedfrog]

to turn it from a day return to a period return?

I mean the return portion only

The day return is £20 and the period is £24 so it's worth doing if I can, rather than buy a new single at £20

 

[Solent&Wessex]

to turn it from a day return to a period return?

I mean the return portion only

The day return is £20 and the period is £24 so it's worth doing if I can, rather than buy a new single at £20

If you do the XS before the original ticket has expired, yes. So if you noticed during or immediately after your original journey that you wanted a return instead, and then asked the Guard or ticket office to amend it, then yes, you just pay the difference. If you turn up later, ie the next day or week, then no, that ticket has expired and it cannot be altered.