Oh sorry, as you are in Barcelona, I spoke in spanish. Well, you're right, better in english for that the others can understand and follow the solutions and maybe the successes :-)
The steps were very easy, I did the same changes as explained in the readme.html attatched inside the contribution. In fact, there are only 4 steps, 4 bunches of code easy to paste. Two of then in the login.php and the other 2, inserted in the cm_login_form.php file. But as @@greasemonkey says, no success. When login, the price is the same as the Retail price. After that, I put the login.php 2.3.3 (modified with SPPC) and however, and THIS file works properly! But of course I cannot let this file since is not a bootstrapped code, is a <2.3.4 version.
After that, I found your contrib. 9090 and tryied with it, but failed again. Your contrib. seems to do nothing, or I am doing something wrong...
I have a scramble with login.php, products_listing.php and products_new.php because their codes are absolutely different than previous versions, I mean, 2.3.4 versions of these files are so different, and the SPPC instructions for the 3 files are useless, forcing to be set up by an expert developer until a future step-by-step update of SPPC 2.3.4 (for non vanilla files). But now, login.php is the file that makes me worried.