Refresh Whatsapp contacts programmatically
It is recommended that you should not interact with other 3rd party apps unless they provide a handle to interact. Which is already given by whatsapp as openurl scheme.
In case you have the contact that is removed or added you should address the issue first in your app so it doesn't/does initiate the action to open App before evening checking with wahtsapp.
You can use a great library that APAddressBook to do the contact add and modified check.
Obviously you can't. Since WhatsApp's sync procedure is done inside the app itself, you will not be able to do a sync outside the app. What you could try to do is adding the full number with country code in the URL, then parse it to WhatsApp. WhatsApp should do a presence subscription, and so you will be able to send a message to that number.