I have some older projects that were built when I had a weaker understanding of what you could do in dataiku, and I have identified some redundancies.
How simple is it to reroute the starting data set for a flow? How would you handle it so that it would not ruin the old processes but going forward used the datasource?
You can change the input(s) of a recipe to point it to another dataset that you would have previously imported in the Flow. To do so, check the "Input/Output" tab in your recipe screen.
Keep in mind that the downstream processing will only work if the new "starter" dataset doesn't introduce breaking changes, especially regarding the schema.
If you want to "vertically" concatenate records from older data with more recent ones, assuming that the column names and types do not change, you can use a "Stack" recipe. It is different from the "Join" recipe which "horizontally" combines columns from multiple datasets by matching records using a common dimension called the "join key".