Hi Szymon,
I've done things like that, despite I never thought to change the Point Style.
You must change the property for each plot. That is, use a for loop to make active each plot first and then change its properties. Change the active plot on each iteration of the loop (0, 1, 2,... and so on until the number of plots you have) wiring the iteration index to the "active plot property".
Maybe you don't need to use the loop, I needed it in my work, but remember: first make the plot active and then change its properties.
I hope to help.
Andres Menacho
P.D: Don't worry for your English. I have to work it too.