How can I correctly change the upos of words in a sentence using Stanza?

Question

I am using Stanza in order to receive a sentence and change its upos tag so that I can get a more personalized constituency tree. This is my code snippet :

import stanza
import nltk
from nltk import Tree
from nltk.draw.util import CanvasFrame
from nltk.draw import TreeWidget

sentence = "Juan camina al parque con su madre."
pipeline = stanza.Pipeline('es', processors='tokenize,mwt,pos,lemma,depparse,constituency')
parser = pipeline(sentence)

upos_mapping = {
    "NOUN": "Sustantivo",
    "ADP": "Preposición",
    "DET": "Determinante"
}


for sentence in parser.sentences:
   for word in sentence.words:
      if word.upos in upos_mapping:
         word.upos = upos_mapping[word.upos]


parsed_sentence = parser.sentences[0].constituency.children[0].children


print(parsed_sentence, parser)

The problem that I am facing is that when I print the "parser" variable that contains the processed sentence, I get all the upos modified. However, when I print the constituency parser, the upos tags aren´t changed. This is what I get :

 ((sn (grup.nom (PROPN Juan))), (grup.verb (VERB camina)), (sn (spec (ADP a) (DET el)) (grup.nom (NOUN parque))), (sp (prep (ADP con)) (sn (spec (DET su)) (grup.nom (NOUN madre)))), (PUNCT .))
 [   [
    {
      "id": 1,
      "text": "Juan",
      "lemma": "Juan",
      "upos": "PROPN",
      "xpos": "np00000",
      "head": 2,
      "deprel": "nsubj",
      "start_char": 0,
      "end_char": 4
    },
    {
      "id": 2,
      "text": "camina",
      "lemma": "caminar",
      "upos": "VERB",
      "xpos": "vmip3s0",
      "feats": "Mood=Ind|Number=Sing|Person=3|Tense=Pres|VerbForm=Fin",
      "head": 0,
      "deprel": "root",
      "start_char": 5,
      "end_char": 11
    },
    {
      "id": [
        3,
        4
      ],
      "text": "al",
      "start_char": 12,
      "end_char": 14
    },
    {
      "id": 3,
      "text": "a",
      "lemma": "a",
      "upos": "Preposición",
      "xpos": "spcms",
      "head": 5,
      "deprel": "case"
    },
    {
      "id": 4,
      "text": "el",
      "lemma": "el",
      "upos": "Determinante",
      "feats": "Definite=Def|Gender=Masc|Number=Sing|PronType=Art",
      "head": 5,
      "deprel": "det"
    },
    {
      "id": 5,
      "text": "parque",
      "lemma": "parque",
      "upos": "Sustantivo",
      "xpos": "ncms000",
      "feats": "Gender=Masc|Number=Sing",
      "head": 2,
      "deprel": "obl",
      "start_char": 15,
      "end_char": 21
    },
    {
      "id": 6,
      "text": "con",
      "lemma": "con",
      "upos": "Preposición",
      "xpos": "sps00",
      "head": 8,
      "deprel": "case",
      "start_char": 22,
      "end_char": 25
    },
    {
      "id": 7,
      "text": "su",
      "lemma": "su",
      "upos": "Determinante",
      "xpos": "dp3cs0",
      "feats": "Number=Sing|Person=3|Poss=Yes|PronType=Prs",
      "head": 8,
      "deprel": "det",
      "start_char": 26,
      "end_char": 28
    },
    {
      "id": 8,
      "text": "madre",
      "lemma": "madre",
      "upos": "Sustantivo",
      "xpos": "ncfs000",
      "feats": "Gender=Fem|Number=Sing",
      "head": 2,
      "deprel": "obl",
      "start_char": 29,
      "end_char": 34
    },
    {
      "id": 9,
      "text": ".",
      "lemma": ".",
      "xpos": "fp",
      "feats": "PunctType=Peri",
      "head": 2,
      "deprel": "punct",
      "start_char": 34,
      "end_char": 35
    }   ] ]

I have not find any resources in the Internet. I would be pleased if someone could help me. Thank you!