When replacing the lamp for a projector, it is important to:

Waiting a few minutes after the projector is turned off is essential because projector lamps can get extremely hot during operation. Allowing the lamp to cool down before attempting to replace it reduces the risk of burns or injury when handling the components. Additionally, this cooling period helps prevent damage to the lamp or the projector itself, as sudden temperature changes can affect the integrity of the lamp and surrounding parts.

When it comes to the other options, leaving the lamp housing on the projector is not appropriate when replacing the lamp, as it must be removed to access the lamp. Disassembling the lamp reflector can lead to misalignment or damage, compromising performance. Lastly, cleaning the lamp with alcohol is not advisable, as it can damage sensitive components and is generally unnecessary if proper handling procedures are followed.