I decided to override membership provider, will my design cause problems later?

 Hi guys, I have started usting ASP.NET recently.
The project I am working has a legacy database(which will be located in different location from membership provider DB). which means I am going to use 2 DB to store user information. One is for the asp.net membership provider and anotherone is for business logic.
( I have to store user's ID/password information into membership provider database, and all other information(address, email, phone number etc) into legacy database .)
After investigation, I decided to
1. create a link(or called as junction sometimes) table which links user_ID(key from asp.net membership DB) with the user's primary key(say customer_ID) from legacy database.
2. when a user try to register with information, I will
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