yes, just upload to C: after you rename them.
but...to boot evox 2nd,
you need to know what order your bios searches for the xbe's on C:
for example:
the standard flavor of the X2 bios boots in the following order,
evoXdash.xbe
neXgen.xbe
xboxdash.xbe
if your using the X2 bios, and havent changed anything, to boot UnleashX first, and EvoX second, simply name Unleashes xbe to evoxdash.xbe, then name evox's xbe to neXgen.xbe.
This is the quick and dirty way to do it, and it'll work perfect, and yes, it can be a little confusing with the name changes and all.
The "proper" way to do it would be to use XBTool and edit the boot order of your bios, then flash the modchip with the new bios. You could then set it to say,....
unleashX.xbe
evoxdash.xbe
xboxdash.xbe
and name the dash's xbe's accordingly.