Do all examination bodies require 5-3-1 / 1-3-5?
The ABRSM does not require any specific fingering for scales and arpeggios.
From the 2021–2022 syllabus section on "Scales and Arpeggios":
Fingering: Candidates may use any fingering that produces a successful musical outcome.
Why do any examination bodies require specific fingerings?
As far as my experience goes, no examiner will be looking at your hands anyway! Often, the piano keyboard itself is physically out of sight for the examiner. Their job, in an exam, is to listen to what you play. There is no good reason to always use 1-3-5/5-3-1 at all. Some triads are unplayable that way, by some players. It would be unfair to penalise them, ...
Very few people do the accompany tract. Very few pianists are willing to do accompaniments, in general. It competes with teaching in the thank-less stakes. Few people are willing to do specialized training just so that they can be heard and never seen.
You don't even get your name of the candidate's certificate when you do it. Seeing as most people get into ...
The Piano exam will only test your proficiency in playing the piano (most probably a grandfather piano), while the Electronic Keyboard exam will not only test your proficiency in playing the keyboard but also how you use the keyboard functions (Sync. Start, Intro/Ending, Rit., Acmp., etc). I have myself cleared Grade 4 Electronic Keyboard and Grade 5 Theory. ...
I dont see how you are going to do these exams without a teacher. You would have to do the following
and eventually music theory
All of which would be very difficult without the aid of a teacher.
Turn up for the piano exam and you will be expected to play for it on the piano provided. At a keyboard exam, you take your own instrument.Unless your keyboard has a realistic sort of piano feel, you may be thrown, and not do as well as expected.