I get where you are coming from . I just feel that your proposal is a lot of re-rolling for not much utility. What about:
Enchanted Weapon - Once per battle the unit may re-roll all misses in a combat.
Blessed Weapon - Twice per battle the unit may re-roll all misses in a combat.
So it gives you an edge - but only once or twice. You have to decide when to use it so another decision to make - do you use it now against those light foot or save it for later. You could make it that you have to declare either before or after rolling. Before would be weaker therefore perhaps more appropriate.
I was thinking of something similar. A unit with Enchanted or Blessed weapons can choose to use the ability, or not. If they use it, then after wards they roll a D6. The ability is lost for the rest of the game unless they roll a '6' (Enchanted) or '5-6' (Blessed). So a unit can be sure of having the ability once, and if they're lucky may get to use it again. Once it's gone, it's gone.
Your proposal could be costed as a single ability - for each +1pt you spend, a unit gets one reroll of all misses per game. There's some merit in that.
In either case I'd say you choose to use it after rolling.
Enchanted (+1pt) - Unit may treat one roll of 6 per attack as 2 hits
Blessed (+2pts) - Unit may treat up to two rolls of 6 per attack as 2 hits
Venomous (+3pts) - Unit treats all rolls of 6 in an attack at 2 hits