Altering Server files is a big no-no anyway, so that's good :-D. YOu could try using SharePoint designer to create a so-called aggregation webpart, pulling data from all sites in the site collection (which of course get security trimmed by sharepoint, so people see only what they are allowed to see).
YOu can create use a DataFormWebPart in SharePoint designer to build an aggregation webpart. This is still ootb, but allows you to configure the datasource: i.e. have the datasource query the entire site collection for calendar items, then display them in a list. Disdplay them in a "new" calendar will be a lot of work though.
There is no way to "copy" or deisgnate specific calendar items to be visible in specific other calendars, this will take custom code.