If you use the Mod Maker program it creates these for you along with the complete modes needed behind the scenes. Eventually there will be more fields to modify directly inside FG but the form (window) for Items doesn't show everything yet and will require some redesign to handle this.
But to answer your question yes, sort of...
Take a thrown knife as an example. To build it for Melee and Ranged you want to create the type as "Melee Weapon, Ranged Weapon" because it is both. This opens up the ranged fields needed.
Do something like the following:
Damage = sw-2 cut|thr imp|thr imp <-- that is melee|melee|ranged
Reach = C, 1|1
Range (this is the tricky one) = 0/0|0/0|ST*0.8/ST*1.5 <--- this says it is a ranged weapon but the first two attacks 0/0 and 0/0 get matched up with the first two melee entries in the Damage field. The ST*0.8/ST*1.5 are half & max range & apply to the ranged mode.
Rate of Fire = 1
Shots = T(1)
So that creates both Melee and Ranged attack mode however it also creates all three modes in Melee and Ranged so you would then need to delete the extra melee attack created on the Melee combat tabs AND on the Ranged combat tab also remove the two attacks that only belong to the Melee combat tab.
If I feel skippy in the middle of the night I might dig into this and see what can be done to make that work better. If Ronnke doesn't beat me to it of course. But I've been working on adding Vehicles and Animals to the Mod Maker and so far so good.