Changing squawk is a bit of a sticky one. That it alerts controllers of airspace below you is inits favour, but against it is the loss of the data block attached to your "echo", which was the reason given by several of my employers for retaining the given squawk code unless told to change to 7700. But the idea of staying at cruise level depressurised is utterly wrong, unjustifiable and should be ignored. Unfortunately, most airlines have good SOPs and bas, some more of one than the other. Those pilots that have been around a few employers and types, especially those that have a few interesting days out, will know when to ignore an SOP. It's much harder for folk in their first company, especially if that company has an over-onerous approach to SOP adherence.