I can prefix them with an underscore, but it's not something that the Ruby Community knows. I can make them private, and practically brake privacy of those method, by calling them with send.

```ruby
custom_data.send :has_new_properties?
```

Instead of 
```ruby
custom_data.has_new_properties?
```
If the method was private, the first example would pass normally, but the second would raise "private method called".
That would work fine, because send doesn't look at methods access control, but it's not usual way to do stuff like this (well, this is a not a usual use case, however you look at it).