Edit format of Paginate_Links()

There is no clean way to do this (that I notice from quick look at rather messy code of it), but $n_display is passed though formatting number_format_i18n() function which does have a filter.

So you could try something like:

function make_number_into_dot( $number ) {
    return 'o';
}

add_filter( 'number_format_i18n', 'make_number_into_dot' );

// your pagination handling here

remove_filter( 'number_format_i18n', 'make_number_into_dot' );