An electronic NHS prescription cannot be amended once it's been sent to the spine.
If an amendment is required, the prescriber would need to cancel the prescription and regenerate it in amended form.
The only exception to this is when the dosage instructions are not clear. Most pharmacy system suppliers will have the flexibility to allow you to manually amend this so the dispensing label carries the correct instructions.
Following the transition to Spine 2, software suppliers can now make new features available in their systems to amend electronically submitted prescriptions. Contact your software provider to confirm if these features will be available on your system.