Adding cutom code to admin side of drupal

I don’t know if this is possible. If an administrator adds a user or updates a user is it possible to add some custom code to call Sugar CRM? If it is then how do I add the code to the admin side? I have a form for when the user themselves register which calls Sugar but we could also do with Sugar being called if the Administrator adds someone. Is it possible and how would I go about it if it is? Thanks

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