Every year, there is a meeting between tutors and the examination committee, and every year the Examination committee informs the tutors that a list of abbreviation is not required.
This is mainly something that German candidates do because they are used to doing this when writing legal petitions under their national law. It is sometimes also confusing because candidate answers chosen for the EQE compendium also have it in (the examination committees do not edit these answers).
It is not forbidden, but it is not required - if you do it, you will only lose time. How do you know which abbreviations you will actually use?
Your answers are marked by experienced attorneys who know the exam in great detail - they know the questions, expected answers and they know the law.
You do not lose points if you cite A.87(4) instead of Art.87(4) or Article 87(4)
The exam committee has no official list of accepted abbreviations, but we make a list for our candidates which we put in our questions & answers books. I have also included a German list (see separate posts).
These may be used on the exam without definitining them. They are perfectly clear to European patent attorneys who work with the EPO and WIPO materials.
If you use something else that may be unclear (e.g. sjm for subject matter), then write it out fully the first time you use it in your answers.