Pretty certain grenades were used by grenadiers before the late years of the Napoleonic Wars 1814-1815+
And I meant like very early 1800s.
Thus the rank of grenadier became honorary in that regard for the elite soldiers like the French Old Guard.
While it is a nice idea, this is better put into a test as a modification and should be in everyway possible but since these grenades were tossed into enemy lines it should only disrupt and cause light to medium damage in-game, definitely not a one-hit killing weapon else it would be unbalanced. Grenades are chaotic and unwieldy weapons.
I can imagine both sides charging into melee and a grenade is thrown right between allied soldiers and enemy soldiers squaring off.