I believe I had the income contingent payment option on my SL's before they were consolidated, as well as on my new SL's that haven't been consolidated yet.
I don't know how much or if they will skyrocket, but from my understanding it's based off how much you make and is supposed to be a way to asure that you can afford the payments, so I don't think they would balloon out so much that you couldn't afford them.
As far as electing another payment plan after you've selected that, I don't know. Are you still in the 6 month grace period/in deferment/forbearance, or still in school? If so, I'd just call up my lender and/or go to the financial aid office of my school and inquire as to what entails each of them (I remember receiving a packet that detailed the difference, lemme see if I can find it online though, cuz it could be ANYWHERE in this house

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ETA: Here is a link to WF student loans, I would assume others are the same and/or similar (at least in regards to FFELP loans)... It says the interest only option can be asked for at any time during repayment and that each borrower is entitled to 4 years of I/O payments, it didn't say the others could be asked for at any time...again you might want to check with your lender....
https://www.wellsfargo.com/student/loans/re...ent/plans.jhtml(sorry I don't know how to do the link thing in edit)