Sorry for the very late reply @julian !
yes I was rebuilding the templates, it was a misconception by my side, i thought that I could change on the ACP the header and footer and it will affect to the other templates, but i was importing the src template.
Now i'll try to override the e-mail templates using my child theme, is it just create a e-mail folder inside my templates folder?
i've seen that this has been asked before, but why can't you change the e-mail subject from the ACP? i had to modify it on the src template.