Just saw the Howto filter on custom filters (Thanks Ganja!) and thought I would try it out. I already have a custom filter, PGC Easy Grab - pre-supplied with my account, I think. I clicked edit on it to see what it is made of and... it will not tell me!
Could the edit facility be changed to select the components that comprise a filter. Otherwise the edit is almost no better than a delete and rebuild (delete sections thankfully, no the whole thing).