In pop network, I can no longer modify velocity or acceleration of particle after wire a position Pop.

is there any way to make it possible?

is it impossible ?

I'm just guessing but it is likely you have static values in your Position pop, meaning that you deleted the $TX,$TY,$TZ expressions. The Position pop evaluates per frame, as do all pop's and in this case if you have a static value as a position that is what will be provided each frame.
This means any acceleration after the position will seem not to have an affect.

To add to Peter's response, the Position POP literally takes a particle's position and moves it to another position overriding the velocity and acceleration forces.