They already do this with fuses to lock each chip to a specific iBoot, OS, and release[0] set.
Changing the configuration of the chip is unnecessary. iPhones, iPads, and Macs use roughly the same balance of compute. The thing that does need to change is how many cores in each compute device, but they already do this with A17 vs. M3 vs. M3 Pro/Max/Ultra. That already segregates the product lines a bit: iPads aren't getting anything bigger than an M3/M4, Mac Pros aren't getting anything smaller than an M3 Max, etc.
[0] e.g. production devices vs. Apple internal devkits vs. that weird Security Research Device they released a few years ago to compete with Corellium