Force data reanalyzation


I'm new to elasticsearch and I'm trying to figure out its behaviour. Basically I'm planning to use it for more than one language. This means that my analyzers will grow in number and also that they can change. I found on this page how to update settings.

If I want to add a new analyzer, it looks easy. I update the settings and start to use it.

What I can't figure out is what happens when I change the settings of an existing analyzer. I would expect that all the data which was first analyzed with it to be reanalyzed with the updated analyzer. From my tests, I can't even guess a behavior. Sometimes the data gets reanalyzed, other times it doesn't ...

Can you please tell me how should it work, and if I can make it to reanalyze everything ?