You'd have to pull the change if you landed on the wrong lead after the two fences. Generally you'd never pull a horse up on the straight after those fences, you'd do a finishing circle.
There is a type of Hunter class called a Hunter Hack that does require jumping two jumps. If you are just talking about you various Hunter under saddle classes, no, it does not require flying changes, nor are there fences. The general problem is that Hunter flat classes are often called 'the hack class', which can cause confusion. According to Article G316 Other Hunter Classes in the EC Rule book, point 2, Hunter Hack: horses may be asked to jump one or two fences not exceeding 3'6". That being in Canada only of course.
In Equitation classes changes might be called for.
You should be able to find the rules and regs from your National organization. I will say that usually the rules follow from country to country, however, as Hunters are not an international discipline at this time, there may be significant variations. In North America, the rules are the same, I do not know outside that.
For reference, your National Organization, as identified by the FEI is Equestrian Australia, www.equestrian.org.au