After you file

Hi, I'm asking about the statement, "Don't go in and start changing or you will make a mess for yourself."  I filed my return electronically last week and it was accepted by the IRS.  I am getting a refund, and of course I do not have it yet. Just this weekend I received another 1099 DIV that I had forgotten about.  I would like to go in and start my amended return to report this additional income, because I know I'll owe money back to the IRS (in other words, I'll get that original refund but I'll have to give some back) and I want to get that paid before April 15.  I at least want to pay it via EFTPS prior to April 15, even if I don't have the refund by then.  Why will I make a mess for myself if I go into TurboTax to at least start the amendment now, but not file, so I know the dollar amounts owed?  Is TurboTax still communicating behind the scenes regarding status of the return, now that it's been accepted? Can I at least start the process and not electronically file the amendment until I get that refund?  Thanks!