Hello,
you can deactivate buttons through SPRO setting :--
SPRO->CRM->Interaction Center WebClient->Basic Functions->Communication Channels->Define Toolbar Profiles
Here you can customize the toolbar profile, copy default and modify the z profile based on your requirement later you can assign it to functional profile under business roles.
And,
you can find the code for buttons in component CRMCMP_IC_FRAME . Open Pages with Flow Logic header_jscripts.js. check function wsb_handler.
you will find code for all buttons there.
Please check ,you may find something here.
Thanks,
Amit