You can probably use the Plugin you link to:
Knife Models [XP System & Skills Support]
It looks good!
I used the Individual Weapon Model plugin to let users control their weapon and knife skins. It's not got a menu, it's a bit of a clunky solution. But the way skins stack in sh ends up wonky anyway, it's better than nothing!
I heavily modified my IWM plugin to know about superhero levels; so players can only use 'unlocked' skins, and made other improvements:
For player skins I used the CS User Model Menu:
It's very good!
I heavily modified my version of the CSUMM to support superheroes:
You can modify the Knife Model Menu plugin to support superheroes, but it will be a coding challenge!
You can look at how I modify the CSUMM and IWM to achieve this.