gistfile1.txt

#!/usr/bin/python
#! -*- coding: utf-8 -*-

import re

f = open("input.xml", "r")
text = f.readlines()
f.close()

count = re.compile('^.*(?<=\t| )<boot dev=(\'|\")hd(\'|\").*$')
edit_type = re.compile('(?<=\t| )<(kernel|initrd|cmdline).*$')

out_text = []
ignore_tag = ['<initrd>', '<kernel>', '<cmdline>']

boot = False
# Удаление всех тегов из ignore_tag и установка <boot dev=\'hd\''
for x in text:
    if re.match(count,x) == None:
        if  (all(s not in x for s in ignore_tag)):
            out_text.append(x)
        elif boot:
            add_boot = re.sub(edit_type, '<boot dev=\'hd\'/>', x)
            boot = True
            out_text.append(add_boot)
    else:
        boot = True
        out_text.append(x)

f2 = open("output.xml", "w")
f2.writelines(out_text)
f2.close()