Can I change a pre-set icon, i.e. that one for "insert Powerpoint file"

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Hello!

I have spent hours and hours trying to figure out how to change an icon that will be used to display a pdf document that has already been uploaded to Resource Manager.  When I use the “insert powerpoint” icon, and then link the appropriate file, it displays the powerpoint icon.  I would like this icon to say “download now” or have an “down arrow” icon instead.  Am I able to change this, and if so, how?  I tried re-writing the html code, and it displays the icon I want, but I lose my connection to the file.  Anyone have any