Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

Sell a stock and buy a new one
It depends on the broker. The one I use (Fidelity) will allow me to buy then sell or sell then buy within 3 days even though the cash isn't settled from the first transaction. But they won't let me buy then sell then buy again with unsettled cash. Of course not waiting for cash to settle makes you vulnerable to a good faith violation.