Undecided..Is my Future really for me to Decide?

Opportunity has presented itself in the form of a colleague's resignation. His post is vacant. Should I request for a change in portfolio?

There won't be any change to whom I will be reporting to. However, this guy's portfolio is better regarded than the one I currently hold. Instead of operation work and reporting on such trivial stuff (ha!), I will be working where I can put my expertise into use.

I have spoken to my colleague about this, and he is of the opinion that I should request for a change in portfolio. Whether or not the change will be approved is another matter, but at least I gave it a shot. I am however, unsure about the course of action that I should take. If I speak up and fail to secure the portfolio change, I might be blacklisted. There is also the problem that my boss may have a vested interest for keeping me at my present job, in light of the impending changes come 1 Nov, so my possibility of success may be close to zilch.

There is also the problem of another new staff eyeing the position (I heard from the colleague who resigned). She's more experienced than me, so I am not sure if I can beat her, unless I can pull rank by the mere fact of my parent company.

I also have the nagging worry that if my wish is granted and I get the change in job scope, I may be unable to handle the new job.

All in all, I have a self-created headache now. Should I be content about where I am, even though there may be a lack of prospect (but prospects will depend on how I twist it to my favour, rite?)? Or should I head bravely into the unknown, and step on people's toes if I don't succeed? I am confused...SUPER CONFUSED. Tell me what to do.