How can we change vray proxy materials?

arnau

Hello,

I have done a forest with different proxies trees.
To create the trees I followed the instructions from this link below:

Now I would like to change some settings from the trees textures to effect on the Alpha channel.

How could I change vray proxy textures once the proxy is done?

(I want to use the alpha channel for post production in some program like Photoshop)

Thank's in advance!