Yes, it is possible to log a user's IP when registering a user account by enabling the Save user sign-up IP in User Notes option under Configure WAF, Logging & Reporting.
That said, the vast majority of IP addresses are dynamic. After a few hours they are assigned to someone else. I don't see how what you want to do would have any positive impact to your site. If that user still has that IP address and see they are blocked… they will just restart their DSL/fibre modem to acquire a new IP address.
Nicholas K. Dionysopoulos
Lead Developer and Director
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