Pipe Freezing is great for learning to work under pressure

 

Freezing it is unnecessary ,if its an olive that wont stop leaking undo the nut with another pair of hands holding the pipe into the valve ptfe tape it and redo up the nut.If its a combi system drop system pressure to zero 1st.(which is irrelevant to the poster)

 

As above.
Don't freeze the pipe. I've seen a cylindrical shaped piece of ice blow out and make a right mess!

 

Well, the upstairs radiators are still coming on with the water, and moving the actuator switch to the other side just puts the downstairs ones on too!