Here are the complete steps to change the date of a post, to look as if it had been written on the changed date.

  1. Rename the entry's data file name to the desired date
  2. Rename, accordingly to the entry's data file name, the content of the corresponding cat_X.db file in which the entry reside (it seems not to be updated by nb -u all or anything else)
  3. Eventually correct the date in the DATE field of the entry using nb -e #id, correcting the day name too (thanks to the cal(1) utility)

Hum. I think there may be a better way to do this.