Amend a commit being able to edit what was previously commited

Hi, loving SourceTree since I discovered it (and Atlassian products for years).
SourceTree replaced GitX instantly for my daily use.

But there are two features of GitX that I'm missing, so I'm creating two issues there, hoping for them
Sorry if I'm duplicating an issue that I missed searching, or worse If I missed the feature in SourceTree.

The second feature:
In GitX, in the "Commit view" when you check the "Amend" checkbox, the "staged changes" area is populated with previous commit changes.
That way you can use amend to remove code from a previous commit, instead of "just" adding code like SourceTree does.