if you don't have insurance then you can't take it back anyways... can you? but yeah, if you put in a custom rom, and later you decide to revert it, it's doable. Just download the official Sprint Rom from HTC and run the executable. that should do it
Edit: if you want manilla 2d only without loading a custom rom, you can install this:
http://rapidshare.com/files/149290739/m2dinstall.rar
here's more info:
http://forum.ppcgeeks.com/showthread.php?t=37215
i have the official rom with manilla on it. Hope this helps