Redirect, change or replace the "user/register" link How to redirect, change or replace the "user/register" link
to another registration page, such as "civicrm/contribute/transact&amp;reset=1&amp;id=1"?

Why? Because our "Drupal users" are (paid) members, they have to choose a membership type, they get informed about the corresponding fee (and how to pay offline) and have to provide additional member information (postal address, day of birth,...). All this is handled by a civiMember page, which creates also a Drupal user (user name and password), blocked at the beginning (changed to active as soon as payment is received).
We probably have to keep the Drupal user login block, for registered users (paid members) to login.
The easiest solution I think here is just redirect it at the Apache (.htaccess) level with a rewrite rule:

RewriteRule ^user/register$ /civicrm/contribute/transact&amp;reset=1&amp;id=1 [NC,L,R=301]