You can only replace URL as a whole but not a part of it. For example, if you have a plugin URL like “http://YourDomain.com/wp-content/plugins/YourPlugin/jquery.fancyProductDesigner-fonts.css”, then you can replace this with something like “http://YourDomain.com/fpd.css”
For this you have to add following replacement in “replace in URLs” option under replace tools tab:
wp-content/plugins/YourPlugin/jquery.fancyProductDesigner-fonts.css ==> fpd.css
Also, note that it’s not recommended to replace CSS class names and javascript variable names as these might have been used internally by plugins/theme and doing so might break your site’s styling and/or functioning.