Updating Data in Source Lines Form

Hi-

We're on version 11..5.10.  We upload Asset Additions via ADI, then posted via Mass Additions.  We do not import from A/P.

Is there a way to update/change:

 - invoice #

 - PO#

on assets that have been created in this way?   We've tried to use the Source Lines form to update this data, however have been unsucessul (field protected against update, or adding a 2nd line w/ corrected information with no success).   Are there settings that can be adjusted to allow the updating of this information?

Thank you-

T