I don't see a way to do any of this and I use Multirename frequently.
1) Parameters to call Multirename in scripts, user defined commands, or button definitions to automatically load a profile when opened, Activate RegEx search, etc
2) Keyboard Shortcuts when MultiRename is active to load profiles. Currently only the F* keys work when manually editing the search and replace list.
3) Change the default behaviors (RegEx, Replace All, Save Undo Information) in 'Settings'
Edited: Accidentally hit a keystroke to save the post before I finished.