the conclusions that come from assuming that things were more or less the same?
Sure. I'm comfortable assuming that the laws of physics--e.g., the rate of decay of radioactive elements--have stayed pretty much the same through Earth's history, rather than fluctuating as wildly as they would have to for all the calculations of the ages of rocks to be wrong. Just like I'm comfortable assuming that they'll stay pretty much the same tomorrow.
If you want to add an asterisk to every statement about events more than 5000 years in the past to the effect that
* Note: statements based on assuming the laws of nature operated 500 million years ago pretty much like they do now. Also that we weren't all created last Thursday with all our memories intact.then be my guest. Meanwhile, scientists will smile and go on about their work.