My steps are not quick enough, but a macro or Excel won’t be more convenient/flexible as far as I know.
(Use “Quick Launch” if you can not find the commands used below.)
TSV mode.
Select column 1 (by clicking the Column Header above the Ruler).
Copy it. (“Copy Column(s)” command also can be used, when the selection is not the whole column(s).)
Paste it into a new tab.
—————
Now in the new tab:
Find:
^(.+)\n(?!\1)(.+\n)
Replace with:
\1\n\n\2
▲ To insert an empty line between each two groups.
TSV mode.
Select the 2nd (empty) column (by clicking the Column Header above the Ruler).
Numbering: (Enable these 2 options)
Skip Empty Lines.
Restart Numbering after Empty Lines.
After the numbers are added, press “_”.
Delete column 1. (Now only the number_ column remains.)
Use “Remove Empty Lines” command.
Select the column (by clicking the Column Header above the Ruler).
Copy it. (Or use “Copy Column(s)” command.)
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Now go back to the previous tab:
TSV mode.
Position the caret after the 1st tab character. (= before “Mini…”)
Paste.