Information on use of standard functionality is available in the various resources available. It is (mostly) possible to determine what will happen if you update a standard data field. If you’re not sure, its also relatively straight-forward to test this; all you need is a test environment and an appropriate data set.
It gets more difficult to answer “What If” where you are depending on customizations. If I made assumptions that turn out to be invalid, what will happen. Will my customization operate as expected if something changes?
To run an entire test set very time this arises can be very time-consuming, but you can speculate with accuracy, if you can use technical skills to read the code. This allows the functional consultant to make a “best guess” on what will happen if the value in a data field changes. The answer could be “Nothing changes”, “this doesn’t work anymore”, or somewhere in between.