change wp theme

add_filter( 'stylesheet', 'switch_ma_theme' );
add_filter( 'template',   'switch_ma_theme' );

function switch_ma_theme(){
    $isDomainA = strpos( $_SERVER['HOST_NAME'], 'domaina.com' ) !== false;
    return $isDomainA ? 'theme-1' : 'theme-2';
}