While not specifically a 'feature request' for the BBox program as such, the connection will (hopefully) become clear:

The caveat to buying Realtracks in sets (Paks) is that then you don't have the option of installing just your own choices of the individual RT instruments it contains (at least not with the Mac installers). So if you either want to save space by being picky with the installations per circumstances or, as in the case I'm facing right now that brought me here, something has gone 'wonky' with just one particular RT, you are rather lost. So my proposal is this:

As long as you bought the Pak on this site, the site should "know" what you have as a registered customer and allow you to go for any individual RT at no extra cost IF you had already bought it as part of a Pak at some point.

A 'plan b' would be to make the Pak installers allow you to grab just that one thing from it that you need at that given moment, but the Mac installers are problematic enough as it is so I don't quite see that happen.

I don't think you can go get individual RealTracks via your account, but you can get the 'Sets' via a download link in your account. I assume this is different than the 'Paks' you mention.

Log back into your account at the main store (separate from the forums) and check your purchases.
I'd be surprised if this aspect was different on a Mac, I would think the 'Sets' still come with an installer that lets you re-install that set.
In image below, the list goes on well beyond the bottom of the image, listing all the RT Sets I have access to.
Plus it lists my downloads from last year, so any BonusTracks or Bonus material available last year and not this year is still available should I have any issues like you mention.

If by Paks, you meant Sets, this post is completely useless.. I think of Paks as the whole package, like the UltraPak ..
As you can see I don't have to download the entire UltraPak, but can get down to the RT Sets level.

"Paks" contain "Sets", just so we have the definitions, so the above is absolutely warrant and would usually be quite helpful.

Only thing is, as an Audiophile owner from the start, I never got any of these kinds of "Sets" downloads like you obviously have. Instead, my lot all came on a physical drive, with a single "all-in-one" kind of installer, with no pick'n-choose for any individual part(s) of it (that I'm aware of) - and that's precisely the predicament I'm aiming to address here.

Ahh, I see now
(said the blind man as he picked up his hammer and saw)

Appears to be more of an Audiophile issue than a MAC issue.