Blue Diamond Stakes winner Written By will be a surprise runner in the Pago Pago Stakes with trainer Grahame Begg not prepared to run him in a barrier trial on the steeple grass at Randwick.

The colt had been scheduled to have his final Golden Slipper tune-up on Tuesday in one of two barrier trials on the Kensington track.

Rain put paid to those trials and they have been moved to Thursday on the different surface.

Begg had taken the precaution to enter the unbeaten Written By in the Group Three Pago Pago Stakes (1200m) at Rosehill on Saturday and confirmed on Twitter he would run.

"With the Sydney fickle weather coming into play, the trials were moved from the Kensington track to the Steeple grass which is a totally unacceptable surface. The decision has been made for Written By to take his place in the Pago Pago Stakes this Saturday," Begg said.

Written By is the $7 third favourite for the $3.5 million Golden Slipper on March 24 behind fillies Sunlight ($4) and Estijaab ($6).

Performer ($8) has been added to Thursday's trials after being barred following his sidestep in the Todman Stakes on Saturday which caused Hugh Bowman to come off.

The jockey sufferred concussion and will have tests in the coming days to determine when he can return.