To change the AR I prefer to shim the balance rail with a thin (1/8" strip) of thin veneer (see attachment). Put it behind the BR pin to lower the action ratio and put it in front of the BR pin to raise the AR. You may have to adjust the key level or the dip.
Note that a change to the AR will change inertia (as well as BW). Since inertia is primarily a function of the AR and the hammer mass any change to the AR will change the inertia.
The key at rest actually sits on the backside of the BR punching and as it is depressed it rotates onto the front side of the punching. The key ratio, therefore, is actually changing through the key stroke. So cutting the backside of the punching will slightly move the pivot point forward and raise the key ratio and the AR somewhat. Cutting the punching on the front side only affects the KR after the key contact point pivots forward during the last half of the key stroke which is why it's not as effective as the shim method.
We will feel the most change if what we do affects the AR at the beginning of the stroke rather than at the end because inertia is more of a factor when we are initiating movement. Therefore cutting the backside of the punching to raise the AR is more effective than cutting the front of the punching to lower the AR.