Yes you are right.

To change the plugin to your needs must edit the Install.pm

change line:
$mgr->install_hooks ( 'Welcome', [ ['do_user_validate', 'PRE', 'Plugins::GForum::Welcome::pm', 'LAST'] ]);

to

$mgr->install_hooks ( 'Welcome', [ ['insert_user', 'PRE', 'Plugins::GForum::Welcome::pm', 'LAST'] ]);

Not tested but must work

Cheers,
Boris

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