changing illegal characters in filenames

I have a script that work just fine…
It flushes out illegal characters in a filename, as well as count the characters and alert the user if the count is over a script defined amount

I was wondering if anyone knows of a quick way to make this script ignore the extension of the file, because I would like to include a period as one of the illegal characters that the script will flush out, but because the files have .pdf, .qxd, .eps etc

Also, is there any way to make this script even faster, maybe through some other search and replace method…just wondering what other solutions there are for this same problem

here’s the script I have, it’s a droplet

on open (listFiles)
	--Call To Check Name Length For Max Allowed, And If Too Long Ask User To Rename--
	tell application "Finder"
		my setName(listFiles)
	end tell
	--Clean Any Illegal Characters Out Of Name--
	tell application "Finder"
		repeat with i from 1 to count of listFiles
			set elem to (item i of listFiles) as string
			set fileItem to alias elem
			set strName to name of fileItem
			set replace_strings to ¬
				{" ", "  ", "-", "_", "__", "~", "`", ":", ";", "!", "@", "â„¢", "'", "®", "#", "$", "?", "<", ">", "%", "^", "&", ¬
					"*", "(", ")", "=", "+", "{", "}", "[", "]", "|", "\\", "/", "'", ",", "\""}
			repeat with this_replace_string in replace_strings
				set strName to my FixName(strName, (contents of this_replace_string))
			end repeat
			set name of fileItem to strName
		end repeat
	end tell
end open

on FixName(currentName, fixString)
	set AppleScript's text item delimiters to fixString
	set listName to every text item of currentName
	set AppleScript's text item delimiters to "_"
	return (listName as string)
end FixName

--Direct Controller for Name Length--
on setName(fileList)
	tell application "Finder"
		repeat with thisItem in fileList
			set item_name to name of thisItem
			set item_container to container of thisItem as string
			if kind of thisItem is not "Folder" then
				set name_length to count item_name
				if name_length > 22 then
					set the_error to "This file's name has too many characters. It has " & name_length & " characters, but the limit is " & 22 & " total. "
						set item_name to text returned of (display dialog the_error & "Please enter a new name:" buttons {"Proceed"} default button 1 default answer item_name)
						set the_error to ""
							get (item_container & item_name) as alias
							set the_error to "A file with the name \"" & item_name & "\" already exists. "
						end try
						if the_error = "" then exit repeat
					end repeat
					set name of thisItem to item_name
				end if
			end if
		end repeat
	end tell
end setName