XPath is something

use_external_audio.py

from lxml import etree
import glob

def externalize(sound_info_file, streamed=True, bitrate=96, stereo=True):
    sound_info_file = sound_info_file + ".sound.gmx"
    sound_info = etree.parse(sound_info_file)
    sound_info.find("/compressed").text = "1"
    sound_info.find("/streamed").text = streamed and "1" or "0"
    sound_info.find("/bitRates/bitRate").text = str(bitrate)
    sound_info.find("/types/type").text = stereo and "1" or "0"
    sound_info.write(sound_info_file, encoding="utf-8", pretty_print=True, xml_declaration=False, with_comments=True)

project = etree.parse(next(glob.iglob("*.project.gmx")))
sounds = project.xpath("/assets/sounds")[0]

for sound_info_file in sounds.xpath(".//sound[contains(., 'snd_samplesound')]/text()"):
    externalize(sound_info_file, streamed=False, bitrate=64)
externalize(sounds.xpath(".//sound[contains(., 'snd_testtrack_')]/text()")[0], streamed=False, bitrate=64)

for sound_info_file in sounds.xpath("./sounds/sounds[@name!='sfx']//sound"):
    streamed, bitrate = True, 96
    if not sound_info_file.xpath("./ancestor::sounds[@name='music']"):
        streamed, bitrate = False, 64
    externalize(sound_info_file.text, streamed=streamed, bitrate=bitrate)