Question on calendar and ICS file

The iCalendar specification outlines what is required in an .ics file. In short, a simple .ics file looks like this:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//hacksw/handcal//NONSGML v1.0//EN
BEGIN:VEVENT
UID:19970610T172345Z-AF23B2@example.com
DTSTAMP:19970610T172345Z
DTSTART:19970714T170000Z
DTEND:19970715T040000Z
SUMMARY:Bastille Day Party
END:VEVENT
END:VCALENDAR

The UID is a unique identifier. It's mostly used for sequencing multiple iCalendar requests. The iCalendar specification gives guidance for how to create it:

A good method to assure uniqueness is to put the domain name or a domain literal IP address of the host on which the identifier was created on the right-hand side of an "@", and on the left-hand side, put a combination of the current calendar date and time of day (i.e., formatted in as a DATE-TIME value) along with some other currently unique (perhaps sequential) identifier available on the system (for example, a process id number). Using a DATE-TIME value on the left-hand side and a domain name or domain literal on the right-hand side makes it possible to guarantee uniqueness since no two hosts should be using the same domain name or IP address at the same time. Though other algorithms will work, it is RECOMMENDED that the right-hand side contain some domain identifier (either of the host itself or otherwise) such that the generator of the message identifier can guarantee the uniqueness of the left-hand side within the scope of that domain.

Most calendar applications are pretty forgiving of malformed .ics files. If your events are pretty simple (no recurrence, no invitations, etc), it's probably not too difficult to knock together an AppleScript (or whatever scripting language you prefer) to create these for you. Here's one AppleScript for it from StackOverflow.

You should be able to change the calendar it's in, so I don't understand why you can't do that, but I have encountered events I could not edit before & for me, it turned out to be the fact that the event was owned by someone else (even though I imported it on my personal calendar).

I found out that by opening up the .ics file in Text Edit.app and removing the lines which signify ownership before importing, I could edit the event just fine in the Calendar app. Just removed entries containing ORGANIZER, UID:, ATTENDEE, and/or PARTSTAT. Save and then double-click the edited file.

I created a folder action for it, so all I have to do is drop the .ics file in the folder to import an editable event.