You can change patterns by up to one full increment by switching loads.
There's also some variance in what we can call Modified.
In theory, it's 20 POC. But, if it's designed for a.729" barrel and is in one that's .726" and made a little tight, you may end up with 25 POC instead.
That's why we pattern and test.
I had some tubes measured a while back. Three Remchoke mod tubes here varied by 4 POC or so. All shoot well, given proper ammo.
If I'm shooting clays with an 870, it's Light Mod (15 POC) unless I'm doing skeet or Olympic trap.
Chances are if I'm shooting with the Beretta, one of the chokes will be LM again.