I’ve been automating the setup using editor scripts for [UFPS : Ultimate FPS], a Unity package that provides a First-Person-Shooter platform. [Manual] [Forum]
When setting up characters, some guns have arms attached which necessitates needing to hide the existing player arms. The UFPS manual has a guide for the proper way to [hide arms and the head].
The Unity Asset Store also has [FPS Mesh Tool] which can also mask out the head and arms.