Custom popup for Create user name and other profile fields

In one of our communities, we have SSO enabled but have allowed the users to navigate without creating a username, they are not prompted to create a username unless they click on any action buttons such as reply button on posts etc. We are now in the process of implementing a new registration flow where as soon as the user clicks the action button, we show them the popup (A custom pop-up), which will ask them to fill their username and few other details. Now, the query is – Is there any way we can detect the action click of the user and present them with this custom popup?

Currently – as soon as user clicks the reply/ action button – they are redirected to the “create a username” page. 

Our workflow would be:

Click reply button > Show pop-up > let the user create login name > proceed to the location.

Any thoughts?