Filter IDOC MATMAS04 by plant

Hi all,

I have configured an idoc in order to send information of materials to an external warehouse. But this warehouse is only from a specific plant, for only one company. When other companies create their materials, my idoc matmas04 is activated anyway, but this material (idoc) must not be send to this external warehouse. Is there a way to filter the activation of change pointers, in order to activate it only for materials of a specific plant?

Is it possible to create a Z FM copying the standard MASTERIDOC_CREATE_SMD_MATMAS, and create a filter here?

Thanks in advance. Reward points to helpful answers.