Snippet to disable the main purpose of BP Reactions to only keep the emoji autocomplete

bp-custom.php

<?php
/**
 * If you don't know how to create/use the bp-custom.php file, please read:
 * https://codex.buddypress.org/themes/bp-custom-php/
 */
// Exit if accessed directly
if ( ! defined( 'ABSPATH' ) ) exit;

/**
 * This is just crazy imho!
 * 
 * Doing the following you are not using the plugin for its real purpose
 * but only keep the activity emoji autocomplete..
 */ 
function do_not_use_the_plugin_for_its_real_purpose() {
	if ( ! function_exists( 'bp_reactions' ) ) {
		return;
	}

	// Force favorite to be handle by BuddyPress
	bp_reactions()->disable_fav_replace = 1;

	// Avoid registering reactions
	remove_action( 'bp_init', 'bp_reactions_register_default_reactions', 1 );

	// Do not register activity actions
	remove_action( 'bp_register_activity_actions', 'bp_reactions_register_activity_actions' );

	// Stop trying to update the reaction count/delete reactions on activity delete
	remove_action( 'bp_activity_after_delete', 'bp_reactions_update_activity_reactions', 10, 1 );

	// Do not add the react button
	remove_action( 'bp_activity_entry_meta', 'bp_reactions_button' );

	// Do not add the reactions container
	remove_action( 'bp_before_activity_entry_comments', 'bp_reactions_container' );

	// Do not add the reactions user nav
	remove_action( 'bp_activity_setup_nav', 'bp_reactions_setup_subnav' );

	// Do not add the popular tab
	remove_action( 'bp_before_activity_type_tab_friends', 'bp_reactions_activity_directory_tab' );
}
add_action( 'bp_include', 'do_not_use_the_plugin_for_its_real_purpose' );

function do_not_load_not_needed_css() {
	wp_dequeue_style( 'bp-reactions-style' );
}
add_action( 'bp_reactions_enqueued', 'do_not_load_not_needed_css' );