Much in the same way you can do a CSSRegistration relative to the
context of a collection:

<SharePoint:CSSRegistration name="<% $SPUrl:~SiteCollection/Style
Library/~language/Core Styles/body_text.css%>" runat="server"/>

I would also like to do a ScriptLink as follows

<SharePoint:Scriptlink runat="server" Name="[Collection]/js/Library"
Language="javascript" />

But I keep getting the error

Cannot make a cache safe URL for "~/js/ImageChange/imageChange.js", file
not found. Please verify that the file exists under the layouts
directory

Can someone please tell me why this is?

If the best way is to copy my custom javascript file into _layouts...
can this be done from within a feature?