Custom Contexts applied to a IAX2 trunk

Sorry if I was not clear....Briefly I want to apply a Custom Context created by the module in PBX1 to the VoIP calls coming from the IAX2 trunk that connects to PBX2.

I have to filter the incoming calls to PBX1 from PBX2, in order that the extensions from PBX2 just can call the IVR extension number from PBX1. Nowadays the PBX2's extensions can call any number from PBX1, and I have to avoid this scenario.

is it possible?

Thanks a lot again!!!