I have a couple of editors sitting on my USB drive from the portableapps.com archive: IcoFX (Freeware) http://icofx.ro/ and Greenfish Icon Editor Pro Portable (Open Source) http://greenfishsoftware.blogspot.hu/2012/07/greenfish-icon-editor-pro.htmlhttp://tinyurl.com/q27vmh9
They're also in Filehippo and Chocolaty archives.
I haven't done much serious work with either of these, but if you install from one of the above archives it's easy enough to test and keep or uninstall them as you see fit.
dt