I'm not sure I follow that last bit - "percy does X" is fine for percy, sure -
the mechanism of renaming things is not unique to percy however - it's just a
different set of flexibility options - with a name separate from the url, you
can use the name to refer to multiple urls and the tool picks from all of them
to pick the actual code it uses - ie it might be a local version,  one in hg and
one in git - the package name is an indirection from the url, and it makes some
things easier and some things harder, is all