Question: Related: [When is it allowable to change the rules?](https://codegolf.meta.stackexchange.com/q/1346/3808)

As noted in the linked meta post above, it's typically particularly frowned upon to significantly change the rules of a challenge after posting it. There's no hard and fast rule on this yet, so the purpose of this meta post is to enact at least some kind of **policy to determine when drastic edits should be rolled back**.

Here, we define "rule change" as not any type of edit but **any edit that causes one or more reasonable hypothetical answers to become invalid beyond repair**. Note that the "beyond repair" clause means that this *does not include* minor rule changes such as input/output format. Note that the wording of this definition also (intentionally) does not include edits that give answers *additional* liberties.

There are a few "poll-style" answers here to vote / comment on:

* [Should rule changes that don't invalidate existing answers be allowed?](https://codegolf.meta.stackexchange.com/a/7778/3808)
* [Should rule changes that invalidate one or more existing answers be allowed?](https://codegolf.meta.stackexchange.com/a/7779/3808)
* [Do rule changes in comments count?](https://codegolf.meta.stackexchange.com/a/7780/3808)

Adding your own answer is encouraged, though, possibly addressing some of the following questions:

* Exactly what it says in the title: If you do think that some rule changes should be acceptable, which ones specifically and in what situations?
* If we're going with "rule changes are only allowed if they're minor enough," how do we define a "major" rule change?
* If you think the policy should be something other than something that was mentioned here, what is it, and who gets to decide which rule changes are allowed?

Answer: 
In support of allowing rule changes that invalidate existing answers
====================================================================

**Closing loopholes**

Suppose you've posted a [fastest-code](https://codegolf.stackexchange.com/questions/tagged/fastest-code "show questions tagged 'fastest-code'") challenge about finding factors of integers. Suppose the description of the challenge is "You will be given a positive integer. You must output a proper factor of this integer as quickly as possible."

Now, suppose that someone answers with a submission that always returns 1. Technically, this is a valid solution to the challenge as stated. However, it is a trivial solution, and nothing of value is lost by changing the question to say "proper factor greater than 1". This does invalidate the existing solution, and it is a rule change, but it brings the rules in line with the clear intent of the poster and improves the challenge with no real loss.

Obviously, there is a fine line between closing loopholes and real changes to the rules, but we should allow closing loopholes, even if answers which exploit them have been posted.
Rule changes in comments are equally valid as those that have been edited into the actual post.

*(Upvote if you agree, downvote if you disagree, and comment for anything else.)*