An update in case someone is interested. Audacity would apply a preformed EQ curve to correct the pre-emphasis, it's described in the thread ironbut mentioned. Some of the things aren't the same in the current Audacity version, but creating the xml file with the curve and asking Audacity to use it is rather simple and similar. Audacity performs the equalization first over the file, then you can play it but it won't be altered if you don't save changes (I'm hoping).
It's interesting looking at the spectral analysis plot, the change is rather noticeable after the de-emphasis is applied. Still open to try other alternatives. I've tried to do it on SoX using just the play and deemph commands, but it's not working, it always complains about the filename or some other shit. I really suck at Terminal console syntaxis, I have no idea why it's not working. I not even was able to get SoX converting the file into a de-emphasized one