Is it possible to encode different URLs by myself?

Yes. You can use NXP's TagWriter app to encode different URLs onto your tags.
This can be done using a .CSV file that can be uploaded into the app.

Step 1: Create your CSV file on you device
Step 2: Open the encoding app, I've used NXP tag writer. Click on 'Write tags' , 'Write from CSV' and then select your file
Step 3: Present the tags one by one to the phone to encode.
Step 4: Come out of the app and test the encoding.

Seritag also offers variable encoding services where we will encode your tags for you.
Seritag - 20 Jan 2023