No. Railcards cannot be applied to Seatfrog upgrades.
How Railcards work
Railcards can only be used when purchasing your original rail ticket in the Seatfrog app.
Railcards do not apply to:
Upgrade auctions
“Upgrade Now” purchases
Instant upgrades
Why Railcards don’t apply
A Seatfrog upgrade is an additional purchase that moves you from Standard Class to First or Premium Class.
Railcard discounts apply only to eligible rail tickets, not to upgrade products.