import re
s = '''<Operation dedupMode="normal" name="update">'''
print(re.sub(r'(dedupMode=")(?:normal|accept|manual|review)(")', r"\1manual\2", s))
aW1wb3J0IHJlCnMgPSAnJyc8T3BlcmF0aW9uIGRlZHVwTW9kZT0ibm9ybWFsIiBuYW1lPSJ1cGRhdGUiPicnJwpwcmludChyZS5zdWIocicoZGVkdXBNb2RlPSIpKD86bm9ybWFsfGFjY2VwdHxtYW51YWx8cmV2aWV3KSgiKScsIHIiXDFtYW51YWxcMiIsIHMpKQo=