Override variables in Client Signup Email email template

[AAcat]

Hi whmcslovers,

i'm developing a module with some hooks in whmcs 7.10.x to override some variables in whmcs email template, after some checks in database between two tables, tblclients and custom othern on joined between them.
My goal is try to overrides some $merge_fields whmcs uses normally in its email templates as "whmcs_url". In mine EmailPreSend functions all works great and i can  overrides what i want for all email templates without only  "Client Signup Email", in this email i'm failing my goal and whmcs_url ( for example ) is empty instead override with a custom data.

After a client registration my function check if he comes from a certain state ( for example US ) and assign it to a client group ( i already created in whmcs ), if it is true i need to change whmcs_url with a different value.
Is there a different way  between "Client Signup Email" works with other one and for example "Order Confirmation" email ?
A strange behavior is that if the automatic EmailPreSend ( after client registration ) fail for what i want, if i send this email from his clientarea a second time it works correctly...🙄

Thanks.