I would like to register in Studielink the fact that I am following (or will shortly follow) a given specialisation. How do I go about it?

Some specialisations appear as separate programmes in Studielink; others fall under a general Master’s programme. In the former case you can find the programme directly in Studielink. In the latter case you can resolve this by answering the programme-specific question in Studielink. In this case you first register for the general master’s programme and, later on in the procedure, you will be asked whether you also want to follow a given specialisation.