This is the one which sounds difficult for me. Patterns are fairly global in nature, and they may match synonyms (i.e. methods of the same name but with different meanings), so I'm worried about the mastery of my changes.

For an isNil ifTrue: to ifNil:, it's easy. But for an indexAt: to at: because I'm changing an internal API, I'd like a better preview of what it will affect before launching it (or a way to examine the resulting changes, which is a bit convoluted).

You will see upcoming changes in Changes browser, so you can decide if it's what you really want.

It's like applying refactoring.

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I think this is already available, you just have to use it (or trigger it).

I'm not aware of this kind of things, can you specify where it is available?�

In that case, I would keep the old node, and simply try to find where is the old node equal in the new ast when undoing (or when building the menu to show that an undo is possible on that node).

That's pretty much the same what I'm doing.

Mark