Great Western Coffee Shop

For FGW it is 24th December to 4th January inclusive. An example restriction code:

http://www.nationalrail.co.uk/times_fares/ticket_types/64309.aspx

A reprogramme if agreed, would be split across all TOCs - to change the peak/off-peak restrictions for each TOC wanting it, I understand, is extremely costly for just 4 days - and then switched back again

They should have put notices on the machines advising of this known problem and advising use of only the ticket office pre 0900

Could they not just trick the machines into thinking it was a weekend where peak restrictions don't apply?

Difficult - otherwise you could do the same with banking software, and all hell could break out.

Evidence showed that in many cases passengers found operation of the TVMs was not easy and often counter-intuitive:

Sheer volume of information felt to be overwhelming and difficult to decide where to press.
Passengers felt they had to do the hard work of finding the best ticket for their journey instead of the machine.
Information boxes to the side and bottom of screens were often not seen by passengers.
Information in yellow writing was not readily visible.
In some cases information about routes and restrictions was not provided, instead instructions were given to ask a member of staff for information.
Ages applicable to child fares were not shown.
Jargon was also used especially in relation to the London zone system.

and

Since undertaking our research we have continued to investigate ticket machines and have identified further issues that cause lack of clarity for passengers purchasing tickets:

There is often insufficient information about  restrictions to enable to the passenger to make an informed choice.
There is a lack of coherence between TVMs. On a station it is possible to find a variety of machines all working in differing ways. E.g. One TVM may offer a rail card without requesting a photo card number while another machine on the same station requires it.
At hub and terminal stations TVMs standing next to each other, but provided by differing TOCs, may offer different products. The range of tickets on offer and priority given to them is varied, and from the passengers perspective, without an obvious rationale. This includes not providing tickets to some regional towns serviced by the station. 
Some ticket machines nationally do not provide the option to purchase ticket to relatively local stations built within the last 6 years. Train companies cite the high cost of reprogramming some manufacturers TVMs as a key factor preventing the updating of machines. ATOC have advised they are working to develop an automatic feed to correct this matter but have not offered a date when this development will be in operation.
The presentation of TVMs offers no information as to the range of products available, or whether preference has been given to tickets for a particular route.
Even on unstaffed stations passengers are offered no advice as to what to do if they are unable to purchase the required ticket from the TVM. Permits to travel tickets are rarely available.  This exposes passengers to the risk of unpaid fares, and penalty notices.
Some station have a TVM on one side of the platform only
Some machines take credit cards only

Secondly, if you wanted a Travelcard, you'd need the peak equivalent anyway, as TfL are scrooges and are still charging peak fares

Well BNM, you won't get it.

Firstly, its a concession to the rules, not every TOC has adopted it. Therefore the TOC can offer it for sale anyway it wishes.

The TVM software will need almost a complete rewrite.

They might insert the odd peak train (FGW already do).

It's the same every year. No one has previously raised major complains.

I do have to wonder just how many people travelled on the Anytime tickets during the de-restriction period.

Thanks to BNM for (re)directing me to this thread as I couldn't find it before - just to say having read this thread, I asked my partner what tickets she had gotten from the TVM on Monday-Wednesday between Christmas and New Year, and she confirmed they were all Anytimes. I said that she could have gotten Off-Peaks if I understood correctly, so clarified with BNM who confirmed that to be the case. There were no notices on the machine. We'll be contacting FGW to see what they have to say.

I certainly don't have a good grasp on the train fares as I am sure I have indicated a number of times, but my partner even less so as she uses them much less frequently than I do. I do have to wonder just how many people travelled on the Anytime tickets during the de-restriction period. I am very much tempted to drop a note to our local magazine....

If the ticket office is closed and the machine is only offering peak fares (due to the time), are you expected to pay the full peak fare and claim a refund or would an off peak ticket be sold on the train?

What ticket/journey were you buying? Was it for a journey priced by FGW? If it wasn't, it may have charged correctly at peak price if travelling in those hours?