I guess you mean I need to re-download kfll_setup each time I want to try a new installation. I never thought of that as long as the digital signature was intact. That must really eat up your bandwidth.
No, of course not.
I said: when you see a message on startup about the (for example) KFLL module being corrupted, it means your installed KFLL scenery needs to be updated. The message should also say that you might need to install the Stand-alone Addon Manager, which is what I've said.
You can ALSO obtain the same result by downloading the full KFLL scenery installer, but that doesn't really change much, other then being larger to download.
The Stand-Alone Addon Manager IS able to update your installed sceneries if needed (they need to be installed, otherwise, they are not be found and not updated), that's why the message said so.
I did a new download and installation and all went well - up to the registration. Do I select a REINSTALL or REGISTER SERIAL fron Addon Manager?
IF you are using the current version, there's no difference whatsoever.
They both end up asking your Serial Number. The only difference, is the "Reinstall" will first ask if you have your purchase receipt email, and if you reply NO, it will launch the Esellerate website to retrieve another copy, if you reply YES, it will ask your Serial Number. The "Register Serial" will just ask your Serial Number immediately, but they are otherwise identical.
The first choice said I must have made the purchase within 15 minutes and didn't do anything.
Assuming you are using the current version, it simply means you entered your Serial Number wrong. Wrong, means confusing the letter O with the number 0 ( zero ), or adding extra spaces at the start or at the end of the code, or not putting hyphens. Basically, anything that is typed any differently from the Serial Number as written in the purchase receipt.
And, don't confuse the Serial Number with the Order Number. The Serial Number is a long code that looks like FSDTKFLL-xxxx-yyyy-aaaa-bbbb-cccc, etc. The Order Number is like STxxxxxx. You need to put the Serial Number
The second choice gave me a black screen and hung up from there with a eSellerate Fatal FAILURE message, but didn't crash FSX.
I don't see how they would behave any different, since they do the same thing, except than asking a few question more, in case of "Reinstall".