When voting is on party lines, it may be desirable to 'entrench' the rules by only allowing them to be changed by more than a simple majority. This is because a party in power can often find alterations whose only merit is that they would favour it. In some cases this would force constraints on unwilling voters.
Although it is true that constraints would sometimes have been set by the voters themselves, it is by no means always so. For example, some Church of England elections are subject to constraints that have been set by Act of Parliament. Even where the voters have set them, it will usually be an earlier set of voters who have done so, constraints being set in the bye-laws of the organisation and continuing to exist for many years; the actual voters have no opportunity to alter them at the time of an election.
There is much to be said in favour of rules specifying that at least a certain number of people of particular types must be among those nominated as candidates, but it should be for the voters to decide whether they wish to elect them or not. As soon as they are forced to elect some, the whole election can become distorted by that fact. So I stick to my point of view that, in general, constraints within STV are a bad thing and should be avoided if at all possible. If there is no avoiding their use, the method employed should be as in my article.