Possible to have a per project setting to set certain extensions to a certain grammar?

Is it possible to use a .`editor-config` file and set which grammar it should use?

I don't know if you can already do this but I wasn't able to figure it out by reading the documentation several times. Something like this?
```
extensionConfig:
  pm:
    grammar: 'source.perl6fe'
```
To set all *.pm files in a directory to the source.perl6fe grammar (the scope name of the grammar)