Great Western Railway does allow passengers to pay a fare difference to travel on trains outside their Super Off-Peak ticket's validity window. However, the exact mechanism—whether this constitutes a formal "upgrade" process or simply purchasing a separate valid ticket—and whether any administration fee applies remain genuinely contested among authoritative sources.

In practice, if you hold a Super Off-Peak return and need to travel on the inbound leg outside the permitted window (typically 10:00–15:30 on weekdays), you have two main options. First, you can purchase a separate Off-Peak or Anytime ticket for that leg at a ticket office, on the GWR website, or through a retailer. Second, you can ask station staff to issue an excess fare—a supplement that validates your original ticket for the higher fare tier—by paying the difference between the Super Off-Peak and Off-Peak fares. GWR's National Rail Conditions of Travel reference a "Change of Route or Time" excess fare mechanism that supports this approach.

Critically, whether an administration fee applies depends on the specific fare conditions and the method used. If you refund and rebook the entire return ticket, a £5 administration fee may apply. If you simply pay the difference for an excess fare or buy a separate ticket, no additional fee typically applies—you pay only the fare difference. However, GWR's published guidance does not clearly advertise a standalone "convert Super Off-Peak to Off-Peak" product, so exact costs and procedures vary by date, route, and ticket office.

To avoid penalty fares or on-the-spot charges, arrange any upgrade before boarding. Verify the exact permitted times, fare difference, and any applicable fees with GWR or National Rail for your specific journey date rather than relying on general guidance.