What is the likelihood that God would create one system and then change it to another system before creation week had ended? Why not just create the [final] one first/only and let it operate...?
What I wrote doesn't read there was one system and then it was changed to another system. It reads (or suggests, depending how you interpret it) that during the 6 days of creation, it hadn't rained until day 6. That's all. When you're assembling one whole interdependent system in steps (i.e. the universe), it would be very odd to note the creator "changed the system" before it's even completed.
God had just completed separating the day from the night at the end of day 4, notably the sun. It's a time-consuming process for water to evaporate, rise some 3+ miles into the atmosphere, and then only when certain conditions are met does it rain. One might assume at one point during creation, the sky had zero moisture. I imagine it would take some time to fill up. So, some suggest Genesis 2 reads it first rained on day 6. Not sure why one would think that suggests God decided to "change to another system".
You might find this interesting... When I was looking at some commentaries on the rainbow account, I came across one that asserts Gen 2:5 means it rained:
Keil and Delitzsch Biblical Commentary on the Old Testament
The establishment of the rainbow as a covenant sign of the promise that there should be no flood again, presupposes that it appeared then for the first time in the vault and clouds of heaven. From this it may be inferred, not that it did not rain before the flood, which could hardly be reconciled with Genesis 2:5
But of course, as we've said, there's many things like rain where scripture isn't detailed on issues, or may have different interpretations, sometimes a mass of scholars split down the middle. God has it figured out. All glory to God.