I don't know something that does exactly what you want it to do aside from multiple installations, but I use different characters that want very different UI setups, and my solution has been to use Discord Unit Frames (DUF) for party frames, Discord Action Bars (DAB) for bars and buttons, and CT for miscellaneous mods (CTmail, CTRA, map mods, etc...)
DUF and DAB are 100% customizable. You have just enough room for a 3x5 matrix of buttons in this spot on your UI... you can do that. You want to add a frame for your target's target, you can do that too (coolest thing ever for pretty much any class). Don't need to see party debuffs? turn them off, etc...
For example, my warrior wants to be able to tab through targets and quickly see how many sunders have been applied, and he needs to know healer mana so he knows when to take a break and when it's okay to push forward. So party mana bars are large and mob debuffs are set to be truly gigantic, I can very quickly see exactly how many sunders there are when the sunder icon is freaking huge, and that is made possible by customizing other things smaller to make room for the mob debuffs to be huge. Party buffs and debuffs are set pretty small. He never needs to see any pet info, so pet bars and such are totally hidden.
My Priest, on the other hand, doesn't care about mob buffs at all, so they are set very small. He cares about party life bars, party debuffs and how much health healed, so life bars are large and display current life, max life and amount of healing needed to be healed full so I can choose correct ranks of healing spells appropriately. Party Debuffs are also large, so if a dispel or Cure Disease is necessary, it gets my attention. Pets are important too, so there is a place for party pet bars. He also utilizes the ever-important 'hide party frames when in a raid' to free up screen space, and then the CTRA bars can go where the party frames used to be... where you're used to looking for health bars anyway.
There is an option in DUF to save / load user settings once it's set-up. And you can save individual UI setups by saving just one file in the DUF folder, so your set-up doesn't have to be re-created from scratch at each new version or patch. Each user spends some time customizing, then they are set and everyone can load their settings.
That solution would require converting the people who share your computer over to DUF, but that should not be difficult. Everyone I've introduced to DUF were previously CT or Cosmos users and they ALL switched to DUF, keeping some of the utility mods from their previous mod package.
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