My impression is that hyakushiki kannon is meant to be intentionally confusing and absurd. Logically speaking, it can't fit into any category. To begin with, the statue certainly does not use enhancement which is as far as we know netero's main nen type. The situation gets particularly absurd because netero's particular nen school actually encourages people to build around their main nen type. The manga has specifically shown us the result of using nen types that are too far away from your own and the waste it represents (through kastro). It does not make sense the technique is emitted simply because if it is emitted then netero is not really using enhancement, his main nen type. The statue would be pure nen which can't be enhanced since in general enhancement works by adding or concentrating nen on stuff to improve its qualities. Adding nen to nen is not enhancement, it is simply adding nen. In this context it would be simply emitting more nen. To add to that, the technique would need transmutation to give it that shape and presumably some degree of manipulation. Conjuration does not make sense either because the statue does not behave like a conjured object. Conjured objects are bound by rules and restrictions. The more strict the better. The implication here is that netero would have a conjured object which has the speed and physical resistance to attack the king and withstand his attacks. However that does not make sense because the only restriction the thing seems to have is the prayer which mostly deals with its movements. On a first look, even that does not seem like such a severe restriction.
With that in mind, as in the thing not fitting into any nen type, I'd say its an acquired specialization. The manga did make the point that you can become a specialization later in life. Netero threw himself into madness and for 10 years did nothing but train and prey. I'd say this changed him in such a way that he became a specialization user. After all, specialization is anything that does not fit into the other categories.
The fact that Netero went through an insane and rigorous training that essentially changed his personality and consciousness in fact may be the change that Toagshi was referring to in order for one to attain specialization Nen. But that's not the case for Netero's awesome Hatsu
Everything about Netero's technique is explained in his flashback to his training. He can effortlessly perform a praying gesture faster than a trained eye can perceive. Giving his training he recieved a sound barrier breaking punch.
The Databook has its discrepancies we all know that to be true, but if Netero is not an enhancer he's a emitter. His Nen type is never officially stated aside from the databook but given the effects his Hatsu shows it's not Specialization which deals with supernatural power unexplainable within the confounds of the natural affinities of nen.
Conjuration creates a visible to naked eye item which is given terms and consitions for its desired abnormal effect. Ex.Kurapicka's chains with mutiple rules & Nen applications, Krotopi's copy ability bodies,items,buildings, Knuv a door and room.
Specialization are awkward powers for Nen users Chrollo Hatsu stealer, Fortune telling Mafiette, Meruem devours Nen + Hatsu, Pakunda Mind reading + memory sharing, Alluka's wishes, Pitou's Doctor Blythe All,Kurapicka's 100% all Nen affinity
All unexplainable within Manipulation,Enhancement,transformation ,emission & conjuration rules
Netero Hatsu emits his aura which takes the form of HK when he prays then he strikes. Emitters Nen yes need to be manipulated and yes they can take on the form of things like Razor's devil or The other guys gorilla not to mention Kurapicka's Chain Judgement that he applies a Nen chain with strict conditions on someone's heart...and yet to be seen Saiyuu monkey zodiacs Hear,See,Speak no evil monkey Hatsu the Nen he emits turns into monkeys and each hit a
You lose one of the 3 mention senses.
Netero Hatsu is Emission. His Natural affinity we can agree to disagree that it may not be enhancement but it's surely not specialization. If you look up on HxH.Wikia in Emission Nen it explains the the basis if Netero's Emission based Hatsu.
^The problem is with Netero's main type. The only information we have is that it comes from a databook but databooks are not always reliable, Alluka was said to be a Manipulator too but she is a Specialist. The Specialisation theory might be true...
It's a shame that we have not informations about things like that, I am still confused about Youpi's abilities.
It's a shame the databook gets stuff like that wrong but we know that Alluka's is an off the wall specialization user with no will or personal application just as a tool. Not to mention A.I Dark Continent possible heritage.
Yupi's ability is Enhancement. His Hatsu is both Ehnacement and transformation enhances his own ant body to grow wings,Extra arms, tentacles or eyes, increase in muscular mass and size.