I'm a bit puzzled as to why this is even questioned. We have creationists and theologians presenting fine-tuning arguments that are supposed to show that there must be a creator. If a problem could be found in the rather meager uniformity assumptions that are made, then such a problem would surely refute the fine tuning arguments.
We measure length (and distance, etc), based on a movable measuring rod. In order for such measurement to be possible, we must depend on some well know behaviors of rigid bodies. One might be able to conceive of a world where there could be nothing that behaved like our rigid bodies. In such a world, there could not be the equivalent of our concept of length.
Once our concept of length is known to be meaningful, then basic properties of rigid bodies can be assumed. Euclidean geometry shows that a great deal can be derived deductively from these very simple starting principles. If, in addition, we are in a world where the concept of inertia can be meaningful, then Newton's laws of motion can be deductively derived. Note that I am also implicitly assuming that there is meaningful concept of time.
I think you are perhaps not recognizing that a great deal can be derived deductively from the mere assumption of the meaningfulness of a few basic concepts. The empirical observations that support the meaningfulness of these concepts are commonplace in every day life. For example, the Noah's flood story, even if it is a myth, provides evidence that length was a viable meaningful concept at the time the story was written.
What we mainly need to assume, to talk about the past, is just that the world was such that a small number of basic concepts were meaningful in the same way (same meaning) as they are today. Most of the other physical concepts are derived from the basic ones.
Gravity is definable (derived) in terms of the more basic concepts. But it is not deductively demonstratable that gravity played a role. However, lots of evidence supports the view that it did. Lots of evidence supports the view that the earth has been in a stable orbit for a long time. That's evidence that gravitation worked the same way as it works now. It is also evidence that the principle of conservation of energy has long been in effect.
What I am trying to suggest, is that the assumptions needed are fairly minimalist, that there is lots of evidence supporting these assumptions, and that creationists implicitly make the same assumptions.
Radioactive decay, likewise, is not deducible from the few basic concepts. However, as already mentioned, there is lots of evidence for conservation of energy. Given basic concepts, plus conservation of energy, we can determine the energy that is released by radioactive decay. If the decay rate had been a lot higher, then the extra energy would have been released. If high enough, the earth would be molten. Again, there is lots of evidence against such possibilities.
I'm suggesting that uniformitarian assumptions are not a likely source of problems for evolution or for geology. With respect to the most basic concepts, creationism makes the same assumptions. For secondary concepts, and even for the primary concepts, there is a great deal of supportive evidence. For dating of ancient events, there is a lot of cross calibration between a variety of different ways of dating.
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