hi javi,
you are following the wrong path here, in my opinion.
what you should do is draw a computation/working zone on your traffic map, so your sites will cover only this delimited area. The traffic and coverage will be limited to your study needs.
Unless of course you REALLY don’t want your sites to cover outside the area. Then you have to modify the downtilt and azimtuh of your antenna (or even your antenna types).
If you design your site to emit with 23dB attenuation, you’ll have serious issues covering indoor areas !!
Yes, it is possible to decrease the emitting power of a cell.