How change a core block label

That is the block title and you can use the blocks.registerBlockType filter in the block editor to change the block title and other settings as well.

So for example, this would change the title to “My Heading”:

function changeHeadingBlockTitle( settings, name ) {
    if ( name !== 'core/heading' ) {
        return settings;
    }

    return lodash.assign( {}, settings, {
        title: 'My Heading',
    } );
}

wp.hooks.addFilter(
    'blocks.registerBlockType',
    'my-plugin/foo',
    changeHeadingBlockTitle
);