Is it possible to implement theme preprocessor on specific template in drupal 8?
If you implemented your own template suggestion then it's as easy as writing a function with the following name:

function THEME_OR_MODULE_NAME_preprocess_field__default__node__node_submitted_by__blogs(&amp;$variables) {
}


The main thing to take care of is to convert the hyphen characters (-) to underscores (_).

Good luck!