override-individual-graphql-resolver.php

add_filter( 'graphql_pre_resolve_field', function( $default, $source, $args, $context, $info, $type_name, $field_key, $field, $field_resolver ) {

	if ( 'content' === $field_key && 'Post' === $type_name ) {
		return 'your override value';
	}

	return $default;

}, 10, 9 );

This example shows how to override the "content" resolver for the "Post" type.

You can see the results of this filter in this screensot, where the "content" field returns your override value for each post returned.