How to re-install ports without removing downloaded source and builds?

[aeiouaeiouaeiouaeiouaeiouaeiou]

 >I think I'd lose my database if I do that and if I do `port uninstall 
installed`

It might be interesting to you: https://trac.macports.org/wiki/Migration 
("Show old Migration procedure" -> "3. Reinstall your ports")

Of course, this does not guarantee that everything will not download 
again (in my case I tried to get rid of the +universal variants).
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