Unfortunately, THEY have to edit their own feeds. And it creates some display problems as sometimes LJ doesn't read the code properly (or vice versa if you're on IJ reading an LJ feed) and it can look messy.

So if the feed is edited, it's for EVERYONE subscribing to that feed, it's not something each person subscribing can edit for herself.

But I'd be glad to tell anyone how they can edit their own feed. It can be set to do a summary, a full post, or a single line.