We have a current customer who has an escrow surplus. However her payment is scheduled to increase based on projected tax increases. She would like to voluntarily give us back the surplus to deposit back to her escrow account which is ok, however she would like us to re-adjust her payment back down to what it was. I'm not sure we should do that. I've looked in RESPA but found no reference to anything like that.

RESPA doesn't explain escrow very well, so your confusion is understandable. Complete an analysis for the upcoming year with the higher taxes (which you probably already did to arrive at the surplus). Add the surplus to the beginning balance and determine if this will be sufficient to meet the increased taxes with the same loan/escrow payments.

You can set her inflow-payments at whatever you need to make the outflow-payments. If she voluntarily wants to allow you take her surplus or adjust her payments, put it in writing (ensuring that it is clear that this is voluntary) and have her sign it.

I discuss voluntary payments and provide a sample disclosure in the BOL Webinar I taught in March 2010. You can find more info here:
http://www.bankersonline.com/bankerstore/index.php?main_page=product_info&products_id=971

Thanks!!