Just in case this would also be useful, the following button "touches" the selected files. (In other word, it sets their Modified timestamps to the current time, like the "touch" command in Unix.)
(See here for instructions on pasting the button definition below to your toolbar.)
<?xml version="1.0"?>
<button display="both" separate="yes">
<label>Touch Modified</label>
<tip>Set Modified Time to Now</tip>
<icon1>49</icon1>
<function type="normal">
<instruction>SetAttr MODIFIED=now</instruction>
</function>
</button>