To clarify myself (I wasn't clear). I had an IF in that post, so it was meant to be conditional. The automatic part is just the procedure on the surface, meaning no publicity. The condition will be communicated behind the door. If not met, there won't be an automatic extension.
As of enough leverage, a treaty is needed. What justification for a possible intervention would be without such treaty if Kim's colleague decide to comply while Kim refuses? The treaty grant China's entering the peninsular so long as there is one person who can act as representing NK government. In the worst scenario China can perform a leadership change by performing treaty obligations at the invitation of NK (with Kim out of power in the party).
Think about the scenario you just outlined.
"A colleague of Kim invites the Chinese Army in, whilst Kim disagrees"
That means Kim has already lost control of North Korea and they are facing a regime change or civil war scenario.
It doesn't matter if China has a treaty with North Korea or not.
No one in the world is going to condemn China for entering North Korea in such a scenario. Most likely, everyone in the world will be applauding how China is removing Fatty Kim, because whatever successor China supports will be far better for the people of North Korea.
That successor will depend on China on his position and there will be Chinese troops in North Korea. And that Chinese influence will be pushing North Korea to modernise and develop on the Chinese model, to give up its nukes and also to talk to South Korea rationally.
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In another scenario, China actually could just let North Korea be conquered by South Korea and the USA.
And when it is clear that North Korea has lost when Pyongyang falls, Chinese troops will be welcomed when they enter North Korea as they will:
a) create a safe zone for NK soldiers and government officials along the Chinese border
b) secure NK nukes from accidental use against SK/USA
Then there will be a negotiated reunification of Korea subject to the end of the US-Korea security alliance, as the US/SK know they cannot win a land war against China.
Otherwise Chinese troops will just stay in North Korea for as long as it takes, and SK will be subject to economic sticks, rather than the economic carrot of China rebuilding Korea.