Please send the bug report with steps how to reproduce. Thanks in advance.

The latest SmartGit 18.2 intermediate build 13079 introduces this feature. You can test it by using 18.2 preview and invoking Help | Check For Latest Build.

That's not possible as I tried to explain.

Ha, I've already implemented the option a few months ago! So I think we could mark this request as fixed.
You wrote to paste the commit ID, so you must already have searched for that commit before.

You already can select a previous commit message. What about prefixing it (optionally) with "Fixup! "?

Just for curiosity: do you use the fixup! prefix to prepare amending a commit using interactive rebase?

I would not use a button - it's too heavyweight - but maybe an entry in the Select popup or the control+space popup?

SmartGit 18.2 preview already contains some Git-LFS commands. What further ones you are missing?

Will be implemented in build 13070.

The external application configured on the "Tools" page ("external tool") only is launched if you invoke it explicitly. Double clicking a modified file will use the matching tool from the "Diff Tools" page ("diff tool"). For an "external tool" the output should be passed to the stdout or stderr channel and use UTF-8 encoding. If there is no "Print Git Version" default external tool for you, please click "Re-Add Defaults".

Regarding SmartSynchronize: no, SmartSynchronize performs the diff, so you would need a script (configurable as "diff tool") that first converts the binary file to a text format and then let SmartSynchronize (or any other text file compare) do the diff display.

You need to select the option "Show output and wait until finished" in the external tool configuration dialog, similar to the "Print Git version" default external tool.