Up to BioStar 2.2.1 users were able to register HID Prox cards as CSN cards (Enroll CSN).
However from BioStar 2.3 and above, you can only enroll as Wiegand cards because that was the originally intended concept of BioStar 2.
Note that the stored ID's in the database are exactly the same, they are just being showed differently with the UI in BioStar 2.4.
The only difference is that you will register the new cards as Wiegand cards, not directly as CSN.
BioStar 2.2.1
BioStar 2.4
Below is a test result to help your understanding.
When enrolling a 26bit card as Enroll CSN in BioStar 2.2.1 the enrolled card showed as below.
When upgrading to BioStar 2.2.1 > 2.3 > 2.4, the authentication still works fine.
The difference was that the card appears as below:
Now in order to see it in Wiegand format you have to go to the menu below to change the settings: 
Be sure to check your current ID# and set it to your desired format. In my case I had a 26 bit card.
My card now appears correctly in 26bit Wiegand format.
In conclusion, if you would like to upgrade to the recent version of BioStar 2, you can upgrade it and then change all the undefined formats as necessary with one click.
You will have to register new users cards as Wiegand cards.
If you are going to upgrade your BioStar 2, please refer to the following link.