The only reference to VFR OTT made in the FARs is as follows:
§ 91.179 IFR cruising altitude or flight level.
Unless otherwise authorized by ATC, the following rules apply—
(a) In controlled airspace. Each person operating an aircraft under IFR in level cruising flight in controlled airspace shall maintain the altitude or flight level assigned that aircraft by ATC. However, if the ATC clearance assigns “VFR conditions on-top,” that person shall maintain an altitude or flight level as prescribed by §91.159.
the referenced regulation is the one says if you fly east you fly odd thousands +500', and if you're flying west you fly even thousands +500'.
You could also look at FAR 91.153, which lists the requirements for a VFR flight plan (VFR OTT would fall under, I believe), including
(5) The proposed route, cruising altitude (or flight level), and true airspeed at that altitude.
Therefore, any deviations to your filed flight plan (such as changes in altitude) would have to be reported.
If you are Canadian, the regulations are similarly vague, it is all a question of interpretation. The government makes and writes the rules, and tries to enforce them, but sadly they often each have their own interpretation too.
In the actual situation, inform ATC. They are happier being in the know, and they will tell you if your extra information annoys them and at what point you should update them again.
For exam purposes, your best bet is to talk to other people who've taken the exam or prep classes, or aviation associations and committees who have a hand in designing exams and their questions. They will know what 'interpretation' the exam marker will mark correct.