How can I seek permanent Personalised Assessment Arrangements, rather than reapplying each year?
A quick review of the link you've shown suggests that the two classes you've listed, personalized assessment and alternative venue, are open to two completely different groups:


Personalized assessment is for students with recognized learning or physical disabilities;
Alternative venue is for international students.


You're effectively trying to conflate the two types of accommodations, by requesting an alternative venue as a means of handling your disability. Based on the response of the chair of the committee, they are proceeding according to this distinction. For this to be successful, you need to be able to explain medically why you need to be at home for the exam period. Raising financial costs as a reason will not be a sufficient reason—by that rationale, you're no different from any other applicant wanting an alternative venue.