<?php
$fileContent = '<div class="panel-body">
{toChangeOne}{toChangeTwo}
{
toChangeTree
}
</div>';
$fileContent = preg_replace('~\{.*?\}~sm', 'myReplace', $fileContent);
print $fileContent;
PD9waHAKCiRmaWxlQ29udGVudCA9ICc8ZGl2IGNsYXNzPSJwYW5lbC1ib2R5Ij4KICAgIHt0b0NoYW5nZU9uZX17dG9DaGFuZ2VUd299CiAgICAgICAgICAgICAgICAgICAgICAgICAgICB7ICAKICAgICAgICAgICAgICAgICAgICB0b0NoYW5nZVRyZWUKICAgICAgICAgICAgICAgICAgICB9CjwvZGl2Pic7CgokZmlsZUNvbnRlbnQgPSBwcmVnX3JlcGxhY2UoJ35cey4qP1x9fnNtJywgJ215UmVwbGFjZScsICRmaWxlQ29udGVudCk7CgpwcmludCAkZmlsZUNvbnRlbnQ7