Gutenberg extend blocks add new class name

Yes, you can do this via the classnames() function.

import classnames from 'classnames';

const withClass = createHigherOrderComponent( ( BlockListBlock ) => {
    return ( props ) => {
        let wrapperProps = props.wrapperProps;
        wrapperProps = {
            ...wrapperProps,
            className={ classnames( 'my-custom-class', props.className ) }
        };

        return <BlockListBlock { ...props } wrapperProps={ wrapperProps } />;
    };
}, 'withClass' );