If the plan allows for after-tax contributions in the first place (not necessarily the re-characterization of them) then can't people can do any percentages they want for either deferrals and/or after-tax (within plan/IRS limits of course)? For example, couldn't I do 10% 401(k) and 5% after tax even though I'm not gonna hit $16,500 with the 401(k)?
And, for re-characterization, doesn't the plan have to allow participants to make them also before it's allowed?