Now back to the original discussion:
1. If 100% dynamic block is an issue, then fix the issue or limit it (even if limiting it makes it work like now), but at least limit it to something a couple of levels higher than what we have now (much higher than 2MB).
2. Such move may need a fork and then SegWit can be even forced "in the same package"
You can't just take and change some variable (or constant) in the code
In fact, you can but your blocks (if you are a miner) will be considered as invalid by other miners and thus discarded by the network, so you will be losing the mining reward every time you find a block and don't follow the "rules". That seems to be one of the reasons if not the primary one why changes, even vital changes are so hard to make in Bitcoin. On the one hand, this is good since it preserves Bitcoin from attempts at malicious changes, but on the other, in the times of change it will backfire and drag Bitcoin backward