By extracting text from a file and replacing with another text

I have a text file, I need to extract a string inside the labels <label>xxx</label> and then replacing with another string in the same position, this condition is repeated several times inside the file.
It's possible to use a macro in excel or notepad ++, or by using python, shell script, it's doesn't matter I can accept all of them in order to reach the target.
Thanks.