Generate file Generic.xaml on having generated the project

Good morning,

I take time trying to divide the file Generic.xaml, so that it is possible to work better on, since there comes a moment in which it is very difficult to work on this one, by what I would like dividing the file in different resources dictionaries and on having generated the project there was generated the file Generic.xaml of the application without having to do:
<ResourceDictionary. MergedDictionaries>
But the file was generating me from the content of other dictionaries. I am grateful to them in advance for its help.