In g_weapon.c, look for this:
if( DotProduct( eforward, pforward ) > 0.6f ) // from behind(-ish)
{
damage = 100; // enough to drop a 'normal' (100 health) human with one jab
mod = MOD_KNIFE;
if ( ent->client->sess.skill[SK_MILITARY_INTELLIGENCE_AND_SCOPED_WEAPONS] >= 4 )
damage = traceEnt->health;
}
and replace by this:
if( DotProduct( eforward, pforward ) > 0.6f ) // from behind(-ish)
{
damage = 100; // enough to drop a 'normal' (100 health) human with one jab
mod = MOD_KNIFE;
if ( ent->client->sess.skill[SK_MILITARY_INTELLIGENCE_AND_SCOPED_WEAPONS] >= 4 && ent->client->sess.playerType == PC_COVERTOPS)
damage = traceEnt->health;
}
This means you don’t just need to have CovOps4, but actually BE a covert ops to get the “assassin” bonus.
Now look for this (same file):
case WP_LUGER:
case WP_COLT:
case WP_MP40:
case WP_THOMPSON:
case WP_STEN:
case WP_SILENCER:
case WP_SILENCED_COLT:
if( ent->client->sess.skill[SK_LIGHT_WEAPONS] >= 4 )
spread *= .65f;
and replace it with this:
case WP_LUGER:
case WP_COLT:
case WP_MP40:
case WP_THOMPSON:
case WP_STEN:
case WP_SILENCER:
case WP_SILENCED_COLT:
case WP_AKIMBO_LUGER:
case WP_AKIMBO_SILENCEDLUGER:
case WP_AKIMBO_COLT:
case WP_AKIMBO_SILENCEDCOLT:
if( ent->client->sess.skill[SK_LIGHT_WEAPONS] >= 3 )
spread *= .65f;
This makes the increased accuracy kick in on level 3 instead of 4 (like it should). It also allows the bonus for akimbo weapons - I think that makes more sense, but your taste my differ 
And if you think those guys just “don’t know how to use coverts properly” I suggest playing with some of them for a bit…