Yes sorry I should remember to call it the 
MultiRename dialog.  I use that or the F2 inline edit & F2 doesn't bring up a new dialog so I didn't differentiate.   

It is MultiRename in both of the above requests - recall & auto-update between passes.
Also -- In MultiRename I notice that a 
saved regex rename doesn't tick the <regex> box when it is loaded.  Perhaps you can add that to the save function?
I will just try to remember what I'm doing until you get to the 
Undo phase of development then!  

I can see any 
undo is a major undertaking, I had imagined this would somehow hook into the logging that you employ in MC.  User selects a log entry & steps back from that - was my thought.  
Given the probable need to group related operations from the log, I guess it's still very complex.
Could a preview pane employ a 3rd party util to save work?  Something like a chunk of Irfanviews' source-code perhaps.  (Assuming the code is able to be shared etc.)
One more for the list - 
Debugger - could the view field auto-scroll with the highlight bar?  At the moment it can disappear from view, requiring manual scrolling.  (Too lazy to step, scroll & think 

)