Lots of interesting (and also diverging) opinions.

My point of view on this is that it's important for us as judges to give players as consistent an experience as we can (1) within events and (2) from one event to another.

The MTR is unequivocal. “Once your decklist has been accepted by a Tournament Official it may not be altered.” This should, in my opinion, be our starting point.

If we allow a change of decklists in an event, then maybe five minutes later someone comes up and asks for a change and we don't allow that, it can cause players to feel they've been treated unfairly. And if the player who changed his decklist assumes it's OK and then shows up to another event a few weeks later and is told it's not, that is also confusing and a bad player outcome. Thirdly, if different judges have different points of view on this, players can also get different outcomes within an event — especially if a judge's ruling that a player may not change his decklist gets appealed and the head judge hasn't thought through and communicated the policy.

Some people discussed customer service. I totally agree with Brian here. We need to give good customer service to everyone in the tournament, and that means that people who take that extra minute to check they've got their decklists correct before they turn them in should benefit from that, just the same as people who know the rules of the game can benefit from, say, putting triggers on the stack in the right order. And good customer service at our event can result in deferring the problem to a future event.

A number of people mentioned the exemption/downgrade for a player calling a judge on himself. There are two points here. MIPG section 1 states "If a player commits an offense, realizes it, and calls a judge immediately and before he or she could potentially benefit from the offense, the Head Judge has the option to downgrade the penalty…". (My emphasis)

This requires three ingredients.

1. A player commits an offense
   Calls a judge immediately
   Calls a judge before he or she could potentially benefit from the offense
   

1. If a player has a legal decklist but wants to change his land mix, or switch a card around, or whatever, he has not committed an offense.
   If a player does not call a judge immediately, he cannot benefit from this exception.
   And if the player could potentially have benefitted from the offense, he is also not able to benefit from the exception. This would include if he could have discussed his sealed deck construction with others.
   

It's worth remembering that the player must call a judge immediately.

I don't agree that this is a “default to fall back on” if we can't find the player's list conveniently — it's our responsibility as judges to educate players that their decklists need to be valid before turning them in.

For Constructed events, best practice is to collect all decklists at a player meeting or at the beginning of round 1 rather than when the players register, to avoid situations such as what Shawn described.

My thought is that this rule is the right rule, but isn't being applied consistently at different events. I earnestly encourage judges to think about this and if they've been in the habit of allowing late changes to decklists, please consider including in your announcements at your next few events that decklists are final once turned in.

Greetings…

In any event that I hold a player's meeting (which is any Competitive REL even, regardless of size), I do not permit a player to make a change to their decklist once it is received unless it is to correct an illegal deck list. At most of my small Comp REL events, the player's meeting is generally quick and simply goes over the basics necessary (this is a Comp REL event; number of players and rounds; prize support; special concerns).

I understand that I may be in the minority in that I hold a player's meeting at small events (at least, that is my understanding based upon feedback from other judges); but this small player's meeting generally avoids any deck list issues.

I am firm believer of following this rule at Comp REL events.

That's my two cents, your milage may vary.
Until that time…

Originally posted by Shawn Doherty:

An error is not “I wrote down X, but I'm actually playing Y”. That is a
change.

I assume you would make an exception for Burning-Tree Shaman, in any event where RTR is legal and GPT isn't, right? :D

For me, I allow changes to fix a potentially illegal list (to allow for the downgrade scenario as described in the IPG). E.g. if a player comes up and says he thinks he forgot to register basic land, or only 39 cards in a limited deck, I will either find the list if logistically possible or make a note of what he thinks is wrong with his list.

I do not allow strategic changes like different mana bases or changing sideboard cards.

This opens a small window for people to submit a 38 card list while they call their friends to decide on the final 2 cards. This seems like a bit of a stretch though, and as a player you risk the judge invoking MTR 2.7 and game-lossing you anyway.