Hello Ricardo
From my understanding, when Rene states that you cannot manually change the p-bit, it means that there is no command that directly manipulates the p-bit. In order to do so, you must do it indirectly using one of the two methods indicated in the lesson.
However, according to this Cisco command reference, in IOS version 15.0(1)M the nssa-only keyword was added. This keyword does indeed directly set the P bit to zero. I will let Rene know to make any modifications he sees fit to the lesson.
Now having said that, in order to set the P-bit, you don’t need to use the default-information-originate keyword. You can simply do it like so:
area 3 nssa nssa-only
This would set the P-bit to zero for all LSAs.
I hope this has been helpful!
Laz