How can I edit Custom Form API? I have created the Custom registration form module using the form API as per the requirements. I have also inserted the records in the database using form alter functions. Now I need to create an edit registration form  for the logged users. 

My suggestion on this is:


Create edit_reg form module with form controls 
Retrieve the records of logged users
Pass the values to defalut value of form controls


Is the above method good? May you suggest me any other method to edit the form API?

I am using Drupal 7.
Why not use the existing user edit form, and use hook_form_alter() to add your fields. That way, you get all the built in functionality, such as password changing etc. 

It would also make sense to make the user registration alterations the same way, instead of creating your own flow, unless it for some other reason makes sense to do it that way.