Can I amend a return after it is accepted but before it is processed?

The amendment will not stop the processing of your original return.

But you can still amend if you now do not wish to apply your refund to next year's taxes.

Please see this TurboTax FAQ for instructions on how to amend your tax return in TurboTax.

you are owed a refund and your amendment must show that, regardless of whether you applied it to next year.

Thank you for responding to my question.  I meant to ask:

is it okay to submit an amended return if the original has been accepted but not yet processed?  

It seems like the answer is yes.  Just making sure.

Thanks again.

It is permitted 

but you are taking a chance because you don't know what adjustments or other changes IRS might make to your filed tax return.