Well, for me the first part of your second sentence was misunderstandable:
You can also design a part to be ‘tool-safe’ … so you can remove material from the mold in key areas to adjust the fit, as it’s harder to add material to a mold once it’s been removed.
What you mean by “tool-safe” is probably to have the material thickness =size of the CAD Model of the molded product on the minimum size for the first go at the tooling, to allow for further honing of the mold to optimize flow. As it is easier to
increase the size of a cavity slightly than viece versa. (You said that in the second part of that sentence.)
mo-i