greps to change endnotes to superscripts

You should be able to control/format all aspects of end notes, including the reference numbers, in the Type | Endnote Options menu. You can both apply a superscript and a defined character style, for example. (I often use something like a semibold sans serif for end note numbers, sometimes with a gray tint to reduce their impact on readability, for example, and tweak the font size, baseline offset and left spacing.)