Is it possible to edit the bobobase_modification_date of an object using dtml or a python script?

Sometimes I have to update an object that was entered into the Catalog say a month ago. However, afterward, when I search the Catalog and display the results according to date, I do not want this object to appear as if it a recent addition to the list.

No it is not. bobobase_modification_time is a ZODB-level attribute that cannot be changed by application code. You should change your object and give it another attribute that holds a date-style value that you can manipulate as you wish, and add the necessary index/metadata column into your catalog to have it indexed as well. jens