First the Sniper only mod Criminal gave you is simple but it should work, just change it's name to zzzzzzzzzzUser-MorphinesSniperOnlyModv1.0.pk3 in case you had another mod for weapons that might conflict with this one.
And to change how many grenade or bullet in every weapon just open the weapon.TIK file and edit it, for an example lets say you want to change how many bullets and grenade in "Springfield '03 Sniper" in simple explanation first open this file (springfield.tik) using notepad or any other editor and scroll down to those lines:
//========================================//
// AMMO //
//========================================//
firetype bullet
ammotype "rifle"
meansofdeath bullet
semiauto
clipsize 5 // <-- After shooting ( 5 ) bullets it will reload
ammorequired 1
bulletlarge 1
sp startammo 5 // <-- After shooting ( 5 ) bullets it will reload
dm startammo 50 // <-- Set the maximum bullets this gun have
sprealism startammo 5 // <-- After shooting ( 5 ) bullets it will reload
dmrealism startammo 50 // <-- Set the maximum bullets this gun have
// Additional DM Loadout
dm additionalstartammo "grenade" 1 // <-- Set how many Grenade the holder should have
// dm additionalstartammo "smokegrenade" 1 // <-- Set how many Smoke Grenade the holder should have
// Additional DM Realism Loadout
dmrealism additionalstartammo "grenade" 1 // <-- Set how many Grenade the holder should have
// dmrealism additionalstartammo "smokegrenade" 1 // <-- Set how many Smoke Grenade the holder should have
It's that simple really.