Can I modify the value of Trailing Stop-loss?

Yes. Users can change the Trailing Stop-loss value until the order is triggered. This gives them the flexibility to adjust based on market changes. This control over the Stop-loss leg is available within the GTT order. 

Additionally, you can modify the price of triggered legs marked as 'Scheduled.' Moreover, if the primary leg is triggered and in the 'Open' state, adjustments to both the trailing gap and stop-loss price are possible only when it is in the 'Scheduled' or 'Open' state.