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Changes between Initial Version and Version 1 of Ticket #21699, comment 6

initial	v1
1	1	I am just copying from #21698, to make things more clear here. So my comment how I see that unregistering could help:
2	2	> So there are two ways to allow making custom subclasses of models which should not be registered. One is to somehow allow some configuration in Meta (#21682), another is to call current metaclass which adds it, but be able to remove it from registry immediately afterwards (a bad side-effect is that registration signal has been already made).
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4	4	I didn't know about "no-op subclass" approach. This seems interesting idea.
5	5