Umm--I think there might be a misunderstanding here. Normally you can't trim or adjust one microphone so as to match another one; that's not what this is about. If you have several microphones of the same make and model, then with some effort, you could experiment to find which two are the best-matched pair among them. But most often, when people talk about matched pairs of microphones for stereo recording, they're talking about microphones that were specially selected as pairs by the manufacturer, nearly always prior to purchase. Thus pair matching isn't usually something that the user does--usually it's something that the user buys (or doesn't).
Some people prefer to use such matched pairs when making stereo recordings with two microphones, or with two main microphones plus whatever number of spot or support microphones. In condenser microphones, the capsules are nearly always the part with the greater variation. They convert sound waves into variations in an electrical voltage, and since they have one foot in each of two worlds, so to speak, their task is more difficult and more delicate than the purely electronic part of the microphone. By contrast, even a second- or third-tier manufacturer can build circuitry (or have it built for them) that is highly consistent from sample to sample. But very few manufacturers can make microphone capsules with similar consistency. Even for those manufacturers, the tolerance limits for their capsules are greater as a rule than the tolerance limits for the purely electronic part of their microphones. Variations of 1/10,000 of an inch can influence a capsule's performance significantly, and our ears/brains are more sensitive to left vs. right discrepancies than to microphone characteristics that affect both ears the same.
So for stereo recording--especially with closely-spaced or coincident pairs--the more similar the two microphones are, the better. But there's no standard definition for pair matching. The two microphones in a "matched pair" from manufacturer B could well have more difference between them than a randomly chosen pair from manufacturer A. In addition, age and use can cause the microphones in a pair to diverge from one another; very few old microphones sound and measure the same now as they did when they were new.
--best regards