Not sure if this is true or not, but I have heard rumours that those who do a PhD in astrophysics or particle physics generally seem to have lower job prospects. But what are the statistics like for those with a PhD in experimental solid state or semiconductor physics?

I have a PhD secured at a top 5 ranked university in the UK (I'm a home student) which is due to start during this Autumn term. However, I have had a change of heart and now want to do a Masters in a course that I am really interested in (career wise) at the same university. I realise this may be a long shot; but is it possible to make the switch by just speaking with the course tutor as I missed the deadline for this Masters? Thanks and I appreciate any helpful suggestions.