Hi,

I have a customer who manually installed some scripts on their site and now wants to manage them via virtualmin.

Is there a how-to or post somewhere that explains how I could import an existing script into virtualmin so it shows up under the installed scripts?

It's probably important to note that it's an older version of the script (not the version virtualmin offers)

My apologies if someone has asked this before; it seems like an obvious question, but I didn't find an answer in docs or forum)

Well, that's unfortunately not an easy or simple endeavor.

Virtualmin does certain things to get the app all setup; so it's difficult to import an existing app, as Virtualmin does this and that to get it working during setup.

There is not a Virtualmin supported way of doing what you asked.

I've heard that a few people had luck (after some tinkering) by dumping the database from the app they manually installed, installing the app (the same version!) using Virtualmin, then importing the DB of the old app into the Virtualmin installed one.

That's in no way supported, and simply trying that is likely to cause problems, headaches, and who knows what else. But if you're feeling lucky, it's possible it'll work; just make sure you have a backup :-)
-Eric