Adicionando uma atualização à resposta de Peter Mounce de: link
O método do Sr. McDonald no final funcionou para mim em alguns segundos, e não tem o envolvimento louco da chave de fenda . A citação é:
spoke with a very helpful chap at Velux (UK) and removed the blind quite easily. Method was this: 1) With the blind retracted fully, grasp the casing firmly at each end with your fingers at the back (between casing and glass) and thumbs on the front. 2) Now twist/rotate the case up and out (as if twisting case toward top of window frame) and listen for the ‘click’ of the catches releasing both sides. 3) When both catches released – blind should slide forward and out! Tried it and it worked a treat! Obviously no guarantee but was reassured by Velux that if the clips should break on attempting removal that they can supply a new set of brackets for re-installation.