Ammonia was an old additive / alkali for fine grain developers, but has a tendancy to form dichroic fog. It slows speed and decreases contrast. The same is true for Ammonium Chloride. You would have to adjust the pH after adding it and the smell will be pretty bad.
But, there is no "magic bullet" in film processing. Researchers have tried for years to come up with a family of developers that offer the best of all possible worlds to all products and these are either available prepackaged or in formulas that require nothing exotic. For example, Sodium Chloride is used in Microdol-X to get the same effect without the odor and it has a restrainer to prevent dichroic fog.
PE