The internal industry guidance for changes to Advance tickets says that retailers shouldn't charge an admin fee for customers upgrading from standard to first class on the same service as "this is not classed as a change of travel plans":
Weekdays: All TOCs allow upgrade to First Class in the above circumstances. As with other ticket types, charge the difference between the fare already paid and the appropriate First Single (dedicated or inter-available) fare for the journey. No £10 fee should be charged for doing this.
In theory, compliance to this (and all other rules to do with changing Advance tickets) should be verified as part of the accreditation process, but in practice things do slip through...
Moreover, the Advance ticket terms & conditions do not say anything about this situation being exempt from the £10 fee - therefore strictly speaking if LNER do charge you, whilst they would be in breach of industry guidance, they would not in breach of contract with you.
