Hi,

In fact Icy does have an undo feature but it can work only if plugin supports it and unfortunately for now only a (very) few plugin support it (but almost all internal commands does support it).
There is no easy way to know what a plugin does to an image (and even know that it modified it) so it’s not easy to recover the previous state, also saving the whole stack for each step would consume memory too quickly (or only the last step could be reverted).
Still if you want to quickly test settings for a plugin, you can try to use the Protocols instead, many plugin are compatible with Protocols and normally they always try to preserve initial image state (and generating new image for each process).

Best,

– Stephane