Hello Stuart unfortunately I don't think you will be able to get hold of a Class 450/444 guards manual, I would think it would be considered confidential information. But I can confirm that the doors on the Class 455's operated by SWT are released and closed by the guard. 
Routes and traction can vary depending on the depot you are based at, I for example sign most (if not all) EMUs that SWT use, but I do not work on any diesels. I'll have days where I will work one type of train, but then I've had jobs where I have worked a 455, 450 and a 458 in one day.
I hope this answers some of your questions.
Routes and traction can vary depending on the depot you are based at, I for example sign most (if not all) EMUs that SWT use, but I do not work on any diesels. I'll have days where I will work one type of train, but then I've had jobs where I have worked a 455, 450 and a 458 in one day.
I hope this answers some of your questions.