The weights on the bottom will depend on putter length, so the weight of different grips will change the swing weight if there’s a large enough swing from the Matador to the stock grip

Swing weight is a function of a few factors, weight of head, weight of shaft, weight of grip and overall length of club...essentially these are the factors you are dealing with. The heavier the head and longer the heavier the swingweight....conversely the heavier the grip the lighter the swingweight. For most putters the shaft weight is constant so it is not a huge factor in this discussion.

So, all you need to do is weigh your current grip and compare it to the new grip. Assuming you do not change the length of putter you will know how it affects the weight. You can cheat by adding weight to the end of the grip or adding or subtracting weight to the head if you have weights that can be changed or you use lead tape to add weight.

Whoa, thats alot but it will provide you everything you need to know IMHO!