I'm 99% sure that this is impossible, without some changes. This is how it works:
Take weapon name from file( let's say AK47 )
Convert it to lower( ak47 )
Format a string to weapon_( weapon_ak47 )
Give the weapon
Get weapon id from weapon name( CSW_AK47 )
Set bpammo
If you write PlasmaGun, it will become weapon_plasmagun that doesn't exists. Yes, cso weapons just change the proprieties of already existing weapons, so you could edit cso source to apply the effects when a player get the needed weapons, BUT it the menu it cannot be the cso weap name.
It is possible to add a new field in the file: NameForMenu or sth like this. So, you will have PlasmanGun as name for menu, and the weapon that it's replace as a weapon for formating and for doing boring stuffs. Then, you can use xvar/bool/forward/even a native to know when a player get the weapon from the menu and apply effects.