There are some categories (like Casework) that come with a range of starting parameters such as Width, Depth, and Height, which are initially set to be Type parameters.
You’ll notice that when you go into the Family Types dialog that the Modify button is inaccessible (greyed out), thereby stopping you from changing them to being Instance parameters.
The way to get around this limitation is to simply select the labelled dimension (parameter) in the view, then on the Options Bar toggle on Instance Parameter.
