Originally Posted by
corporate-wage-slave
No, it's not rubbish, though my phrasing was perhaps slightly different to yours. The thing you left out is that your Ready to Fly would be corrupted on return to T5 and you risk losing your seat in trying to resolve it. If you tried this with less than an hour to go then the Flight Management would also need to get involved.
Some of these things are really complicated and that's where FT shines figuring out what is and isn't possible. If you have lots of time, many of these 'outre' things are possible (and fun). When you get to the gate, talking to the gate agents in plenty of time is IMO a great idea.