Is there a way I can use a custom model with mesh sdk ?
I only want to query devices one by one from the provisioner smart phone.
This sounds similar to my use case where I will have a single controlling node that will query and send commands to a set of nodes and I really only need the mesh to allow the range of communications to be extended through relaying communications. I don't think you will really be able to use the stack without using pub/sub, it is deeply ingrained into how the stack is built.
You might look at using a vendor model unless your use case has a SIG model that corresponds to what you are trying to transmit. You'll have to dig in and do some reading though, there aren't any examples with vendor models yet and I am still working on getting them working for myself.
Unless I'm mistaken the source for the mesh smartphone app is not released yet, so you may not be able to write an app to communicate with the nodes until it is released.