I see no reason why they cannot send wz7 or y9 aircraft to edge of Japan from east coast an do their surveillance. They have the assets to do similar spying missions and irritate without breaking any rules.
Two problems with doing that.
Firstly, such aggressive action would only serve to ‘prove’ the need for continued US military presence in those countries and strength America’s China-threat claims. The end result is more anti-China unity between SK and Japan. Instead, without that overt external threat, you are seeing the fault lines between SK and Japan crack open every now and again despite the best efforts of the US and their agents in both countries.
Secondly, by reciprocating, China is also in a way legitimatising American FON operations and spy plane probes.
The most important pieces of intel you can gather from such close in surveillance and aggressive probing is to gauge response capabilities/times and probe for weakness and deficiencies in local defences. Useful if you are planing offensive operations for the US, but far less so for China as it has no ambitions for such offensive operations, and any attacks at US bases in SK or Japan would be mostly done by long range missiles anyways, negating the need for such detailed defence posture information.
I think if China wants to push back, it would be far more effective and useful to gatecrash US and vassals exercises instead.
Doing so would be far less overtly provocative to neighbouring countries and also would greatly undermine the training value of said exercises as the US would need to put in place serious restrictions if they don’t want China to hoover up useful intel.