If you use %sel% for your tool instead of c:\temp\%n.log_%dt and run the tool with this macro, you will get what you want.
The macro copies the full name of the current file, pastes it into a new file, reformats the file name to c:\temp\%n.log_ and adds the current date/time. You can modify the format of the date/time string also with the macro. Then it selects the whole string and runs the tool. After the tool has finished, the new file is discarded.
At the configuration of your tool, do not enable save current file or save all files because of the unsaved new file created by the macro. If you want to save the current file or all files, use the Save or SaveAll macro commands for example after command HexOff.
If you want to see which string the macro produce, remove the last 2 commands.
Find Up Select "."
Find Up "\"
RunTool "case-sensitive name of your tool"