Set a specified attribute (e.g. overscan, gate mask color) on all cameras in group

set_attribute_all_cameras.py

import maya.cmds as cmds

gate_color = (0.0, 0.0, 0.0)

def get_cameras_in_group(group_name):
    group_members = cmds.listRelatives(group_name, children=True)
    
    # Filter out cameras
    cameras = []
    if group_members:
        for member in group_members:
            shapes = cmds.listRelatives(member, shapes=True)
            if shapes and cmds.objectType(shapes[0]) == 'camera':
                cameras.append(member)
    return cameras

cameras = get_cameras_in_group("Cameras")

for camera in cameras:
    cmds.setAttr(f'{camera}.overscan', 1.1)
    cmds.setAttr(f'{camera}.displayGateMaskColor', *gate_color)
    cmds.setAttr(f'{camera}.displayGateMaskOpacity', 1.0)

    # Options: 0 (Horizontal), 1 (Vertical), 2 (Fill), 3 (Overscan)
    cmds.setAttr(f'{camera}.filmFit', 1)