As long as the local change doesn't affect the shared details, and as
long as the shared details are preserved (e.g., as a "View original
event details" tab), then there is no need to "change the RFC"[1], and
the very good reasons to give the user the control of his event details
prevail.
Note: Many event organizers are managers or secretaries who have little
knowledge or interest in providing adequate details for an event
invitation; they just want you to "be there" because they said so. The
interest and priorities between inviters and invitees are often very
different, and every invitee has different levels of details that they
want to have in "their" event.
[1] BTW: Referring only to the RFC and ignoring the users' needs is a
major reason OSS often fails to attract a majority of users; and e.g.,
*one* of the reasons why, unfortunately, Internet Explorer 4 + ActiveX
was successful and the "better" Netscape died).