Bulk add the arm64,x86_64 host architecture value to Packages .pkgproj files.

add_hostArchitectures.py

#!/usr/local/bin/python3
"""Bulk adds the 'arm64,x86_64' value as and advanced option for '.pkgproj' files.
Walks all sub directories specified at '[path]' for '.pkgproj' files, makes a backup
file in the same destination.
Does not add the value if a value already exists.

Usage: ./add_hostArchitectures.py [path]

Tested with Python 3.7.9.
"""
import os
import plistlib
import shutil
import sys
from pathlib import Path, PurePath

NAME = sys.argv[0]

try:
    WORK_DIR = sys.argv[1]
except IndexError:
    print('Usage: {} [path]'.format(NAME))
    sys.exit(1)

_PKGPROJS = set()

_ARCH = ['arm64,x86_64']

for _root, _, _files in os.walk(WORK_DIR):
    for _f in _files:
        _path = Path(_root) / _f
        _pure_path = PurePath(_path)

        if _pure_path.suffix == '.pkgproj':
            _PKGPROJS.add(_path)
            _dest_folder = str(_pure_path.parent)
            _backup = Path(_dest_folder) / '{}.backup'.format(str(_path))

            if not _backup.exists():
                shutil.copy2(str(_path), str(_backup))


for _proj in _PKGPROJS:
    with open(str(_proj), 'rb') as _f:
        _plist = plistlib.load(_f)

        if not _plist['PROJECT']['PROJECT_SETTINGS'].get('ADVANCED_OPTIONS'):
            _plist['PROJECT']['PROJECT_SETTINGS']['ADVANCED_OPTIONS'] = {'installer-script.options:hostArchitectures': _ARCH}
            _f.close()

        with open(str(_proj), 'wb') as _f:
            plistlib.dump(_plist, _f, fmt=plistlib.FMT_XML)