Customizing portals registration page

Hi, I want to add more fields in the Dynamics 365 portals page. 

Is there anyway that I can add more fields? I have seen some answers suggesting to create a content snippet for registration page and then setting the values for the custom page in local storage. But the values are not getting saved.

Please do help me with the queries below:
1. Is there any limits for the fields to be added in the registration page?

2. Is there any other ways  of customizing the registration page?

Thanks in advance!!