<?php
$string = 'Hello John, how are you John. John are you happy with your life John?';
$numberOfInstances = 2;
echo implode('dude', explode('John', $string, $numberOfInstances + 1));
Hello dude, how are you dude. John are you happy with your life John?
Output for 8.3.5
Warning: PHP Startup: Unable to load dynamic library 'sodium.so' (tried: /usr/lib/php/8.3.5/modules/sodium.so (libsodium.so.23: cannot open shared object file: No such file or directory), /usr/lib/php/8.3.5/modules/sodium.so.so (/usr/lib/php/8.3.5/modules/sodium.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
Hello dude, how are you dude. John are you happy with your life John?