Experiment for wrapping and changing the prev/next arrows in the WordPress Pagination Block

wrap-pagination-render_callback.php

<?php


/**
 * Experiment to rewrite the render_callbacks of the pagination prev/next blocks to swap the arrow for something else
 */
add_filter('register_block_type_args', __NAMESPACE__ . '\\swap_render_callback', 10, 2);

/**
 * Replace the pagination-prev/next render_callback with a function which wraps the native function's return value
 */
function swap_render_callback($args, $block_type)
{
    if (
        $block_type === 'core/query-pagination-previous' ||
        $block_type === 'core/query-pagination-next'
    ) {
        $args['render_callback'] = __NAMESPACE__ . '\\pagination_prev_next_render_callback';
    }
    return $args;
}

/**
 * Wrap the native callback function
 */
function pagination_prev_next_render_callback($attributes, $content, $block)
{
    $native =
        $block->name === 'core/query-pagination-previous'
            ? \render_block_core_query_pagination_previous($attributes, $content, $block)
            : \render_block_core_query_pagination_next($attributes, $content, $block);

    $newArrow = preg_replace(['/←/u', '/→/u'], ['⬅️', '➡️'], $native);

    return $newArrow;
}