Yes, opening shared.lua you can edit the weapon drop on LootSpawn() function. You can change the weapons on the same function of the drop changing.
Example:

local M4A1 = ents.Create( "weapon_m4a1" ) #weapon entity
if ( !IsValid( M4A1 ) ) then return end
M4A1:SetPos( Vector( 13826, 12370, -7000 ) ) # position
M4A1:Spawn()

#weapon entiy: you will change this line for the your workshop weapon entity name.
#position: changing the vector = changing the weapon spawn position, you can make it random making a table and using math.random function too.

Example to make it random:

Put this code in the beginning of LootSpawn() function

weapon_positon = { Vector( 13826, 12370, -7000 ), Vector( 4232, 2342, -7000 )}

then change M4A1:SetPos( Vector( 13826, 12370, -7000 ) ) to
M4A1:SetPos( table.random(weapon_position) )

Of course, put more vectors on the weapon_position table.

random weapons on spawn added on patch 21 [0.3a]