Thank you for your help! I also asked Communicate-ed – they said this:
Whether the candidate can have ET or SRB depends on what the practical exam involves. For example, you can’t have a SRB in the middle of a performance, and you can’t have extra time to perform a piece that is a set length. But, if the exam involves time for composition etc, it may be possible to have extra time/SBR for this. We suggest you contact the relevant awarding body for advice.