Customers can cancel and modify the unfilled portions of partially filled orders. However, if the original order is fully filled during the modification or cancellation process, cancellation and modification may not be possible.

Orders can be classified into two types based on their validity period:

1. Day Orders: Orders not filled by market close will be automatically canceled.

2. GTC (Good 'Til Canceled) Orders: Orders remain valid until fully filled or completely canceled.

GTC Order Expiration Rules:

Generally, the maximum validity period for such orders is 90 calendar days, after which they will be automatically canceled. For stock GTC orders, if significant corporate actions occur during the order period, such as stock splits, mergers, or dividends, the system will automatically cancel them before market open on the execution day of the corporate action.

Regulators expect brokers to implement control measures to prevent disruptive orders from being submitted to the market. As such, brokers may set price limits on buy orders and sell orders. Note that while these price limits aim to minimize price risks while maximizing order execution, they may lead to delays or unexecuted trades.