I simply use a folder. Changing the MPQ is sort of risky, since you can fuck things up. And more complicated. Although the risk can be mitigated by thinking, aka backing things up, but still.
I just put a folder in the WC3 folder, named "Local"
Then I organize things by author and modelname.
Example:
Local\Alpain\Mage
With icons I put one icon like the example above(main icon) and then the other I put into ReplaceableTextures\CommandButtonsDisabled\Iconname
I've tested and it does work, while still not ruining my system.
Why do I go through all that?
1. Incredibly easy to look up and add models to map.
2. Don't have to import to map and don't have to restart editor.
3. Don't have to keep or make a list of people to credit, as I can just look them up in model paths.
4. Absolutely impossible to NOT know who made a model, because I can't place it anywhere if I don't know the author.
5. If this ever goes into a wider scale, then it's impossible to fake models, as everyone needs to have the same folder and so far it's only possible to get from me.
6. Map space is not used up and memory is only used for models that actually have been used ingame.