A council can change its standing orders, although the standing orders themselves may stipulate a special procedure for making changes. Without the change, the item should continue to be included.
However, most councils have done away with AOB. The problem is that it is not specific notice of a possible decision, and so it is not lawful for a council to make any substantial decision (one that involves expenditure or commits the council to a course of action that would affect the community) under AOB. An alternative is "Questions to the Chairman" which allows any matter to be raised, but helps to make it clear that substantial decisions will have to be made at a future meeting, when they are expressly included in the agenda.