Most of the investment firms I work with do have a change of bene form or will accept a letter of instruction to change the beneficiary on an IRA.
I agree w/bwilk to think about why you have a Roth to begin with. Was the original intent to provide a portion of retirement income? If so, has anything concerning your retirement planning changed to make the Roth unneccessary? (Even if the "math estimate" shows it is unneeded, tax free income later on provides some pretty nice flexibility.)
When college bills arrive, you can use any of the Roth contributions at that time as russthomas suggests. Another option--you can take tax/penalty free withdrawals of those contributions _later_ to help w/student loans and allow a few more years of growth (can't do that w/529).
If financial aid is a consideration the Roth is not included in the FAFSA, the 529 may be to a small extent. If left in the Roth and student loan repayment starts after you are 59 1/2, then you have even greater flexibility to help w/tax free dollars.