"Lock Deck" checkbox option for each saved deck in editor. When enabled, the deck code attached to the deck name cannot be changed until the box is unchecked (i.e. the save&exit button will function as the exit button, and changing to a different deck will not autosave).
In addition to the (valuable) function of preventing people from ruining their decks with their own misclicks, this is especially valuable when the client itself ruins decks due to cards being upgraded or unupgraded (such as with autoconvert). One of the biggest problems with client-ruined decks is that there is no way to prevent the deck being ruined once loaded (as there's no "switch decks without saving" option), so the minute you load your previously fully upped deck that is now 24 cards, there is no way to get back those other six cards. Or, if you, for example, had been keeping historical records of how your deck progressed over the course of the ARC, but you happened to upgrade some cards at some point during that process, all of your old historical decks suddenly would be missing a handful of cards.
Anyways, seems quite easy to implement to me and seems like it would provide a lot of benefits, not the least of which would be probably never hearing me complain about autoconvert ruining my accounts anymore.