Hook to set rules before taxonomy access starts working

Hello,

for drupal 6 I wrote a module, which assigned a role to the anonymous user (automaticaly, without login).
It was the hook_init and it worked with the taxonomy access control module.

function mymodule_init(){
if($GLOBALS['user']->uid==0){

$GLOBALS['user']->roles[17] = "my_role";

Now in the TAC-Version for Drupal 7, it does not work anymore.
It seems that TAC gets the roles before the hook_init is done.
Is this right?
In which hook I should insert my roles-assignement to get TAC to read it?

Thanks and regards

Adriana