<p>How do I programmatically reset the Excel <code>Find and Replace</code> dialog box parameters to defaults ("Find what", "Replace with", "Within", "Search", "Look in", "Match case", "Match entire cell contents")?</p>

<p>I am using <code>Application.FindFormat.Clear</code> and <code>Application.ReplaceFormat.Clear</code> to reset find and replace cell formats.</p>

<p>Interestingly, after using <code>expression.Replace(FindWhat, ReplaceWhat, After, MatchCase, WholeWords)</code>, the <code>FindWhat</code> string shows in the <code>Find and Replace</code> dialog box but not the <code>ReplaceWhat</code> parameter.</p>

You can use the following command to open the "Replace" dialog with fields filled:
Application.Dialogs(xlDialogFormulaReplace).Show -arguments here-
the argument list is
find_text, replace_text, look_at, look_by, active_cell, match_case, match_byte
So far, the only way I've found to 'click' the buttons is with SendKey.
After much research and testing, I now know exactly what you want to do, but don't think it can be done (without SendKey).  It appears that there is a bug in Excel, that won't reset the replacement value (from VBA), no matter what you try and set it to.
I did find this 'faster' way someone posted on MSDN, so you might give it a try.
Faster than Replace