You could do it...but it would make them half as strong. Better to do one 40 day working with one affirmation and another one with another 40 day affirmation.Hail Satan!
If you mean for programming one construct/pool of energy, no, stick with one.
If it's for separate workings, it's fine. I'm doing 5 affirmations for different workings at the moment. Protection, attractiveness, some psychology things.
It's like this: You are building a house and you have a set amount of wood each day. If you are going to use a particular bit of wood and cut it for a door, you wouldn't want to pull it down and re-cut it for something else - a window. You'd use another piece of wood for that.
You could do it...but it would make them half as strong. Better to do one 40 day working with one affirmation and another one with another 40 day affirmation.
Hail Satan!