Canonically, such techniques are fairly well guarded, but more by tradition that anything else.

Assuming you have access to L5R 4e Core rulebook, reference the "Multiple Schools" advantage on page 151- this advantage is required to go to multiple schools.

Also reference page 105, "Insight rank 6 and beyond," where it explains precisely what happens after you get all five levels of your school- you can get Multiple Schools for free, in order to start learning at a new school... starting from the first technique.

In short, you cannot "cherry pick" school abilities at all. Especially as a Ronin- here is where the tradition bit comes in.

Each school has a focus, theme, and pattern. The Kakita Duelist school, for example, emphasizes first strikes and usage of the Center stance- as well as being the premier school for dedicated Iaijutsu masters. By contrast, the Matsu Berserker school teaches skills that focus on the Full Attack stance and beating the ever-living bejeezus out of whatever poor schmuck encountered you today.

Now imagine trying to cherry pick the Matsu berserker rank 3 ability after staying at the Kakita school for 2 ranks- how would the knowledge of the Kakita school have prepared you for the Matsu school? Answer- it didn't.

Moreover, note that each of those schools has a name associated with them- Kakita, Matsu, Daidoji, Yoritomo, what have you. This is because these schools are associated with Samurai families. Canonically, these families tend to be uptight. They will not allow some ronin fresh out of the forest to study with them. Their samurai students usually start school at the age of six to nine, and "graduate" with their rank 1 technique by the age of 14 to 16.

A ronin bandit/bounty-hunter/whatever with however great self-taught knowledge, by contrast, is rough, uncouth, and has no right to these traditional teachings, preserved for generations.

A good example of the "perfect ronin warrior" would be Ikoma- he was sworn to Akodo, the Lion kami. His most recent stats, provided in the 4e supplement "Great Clans," page 119, pegs him at Insight Rank 9- because he has so many skills.

But he has no school ranks, no ronin paths. He's just a BAMF.

Personally, if I were your GM, I wouldn't allow you to cherry pick abilities. I'd allow you to select Ronin paths, and then probably allow you to generate one or two balanced ronin paths that you could then teach others. But, canonically? That doesn't happen much.