Is there away to make CC only show in a specific collection, thus not showing in the catalog?

There is. I think you have to add it to a collection first (there is a way outside the game, but I've not done it before), and then untick all the category options in the OBJD.

There's a catalog-only version of the shftable OMSPs, in case you want to study the files to see how they're edited.
https://www.modthesims.info/d/325570

I have not tried it myself yet, but I bookmarked this when I saw it a few weeks back because I thought it would come in very handy because I have a few retail sims business sets that really clutter the catalog when ya don't use them all the time.

http://nanashi.sims2.net/?p=205

Out of all the Sims 2 categorizing programs I have, of course that tutorial has to require the ONE program I can't bloody get to work on Windows 8.1!

I've been trying to find a non-SimPe way to do this for centuries, so this really made my evening... -.- ~Sarcasm overload.~ I guess the universe is just set on my catalogues being a cluttered mess of crap.

You don't say why you don't want to use SimPE. Is it too difficult to use, or too much work? Changing categories is about the easiest thing you can do in SimPE.

Anyway, it looks like it works exactly like I said. Make an ingame collection, and find the collection file you made.
Find the objects in your downloads (instead of the categorizer), and do the changes in the OBJD in SimPE instead (it's not difficult, just a bit more work since you have to open files separately).

Here's the tutorial I use: http://hugelunatic.com/?p=109. It's for SimPE.

I haven't been able to get SimPE to work on my previous Windows XP computer or on this Windows 8.1 gaming desktop. I have a help thread about it in the creator section, as I've been wanting to create CC for 5 years, like I do for a virtual chat program. Whenever I fixed one problem, it was replaced by another and in the end, I had 10 programs and websites open all at once, trying to work out the issues.

Now I just gave up on it entirely.

Thanks a lot for this though! If I somehow get it to work one day, I can return to this thread to solve my clutter problem.