I thought about this too sometimes but I found it easier to just get to the point, because technically the energies already there, your just directing that energy so theres no need to reaffirm its presence.
Ill give an instance where this got me, I did an affirmation like "In a healthy and positive manner, the suns energy is permanently cleaning my aura from any and all negative energies" and it worked well during it, but when I was finished on the working I noticed when I am not out in the sun or if its a cloudy day that my aura would actually feel very different then compared to being out in the sun. So pretty much what occurred was that the energy I directed and affirmed took the literal meaning of that the suns energies where only cleaning my aura, so on the days and astrological days where the sun wasnt out as much or if it was in its detriment, my aura would also feel the impact because the energies from the working were reliant on the suns. Its not a bad thing persay, its pretty nice knowing being out in the sun can clean my aura as I am out and about, so as a passive type working its great, but for something you want active and to be fair, more reliable, (since the energy you built up for the working is permant), its better to get straight to the point.