In Rally, when you edit a Feature or User story or whatever item, and you want to set a parent for it - it opens a modal called CHOOSE A PARENT. In this popup, you can search by TYPE. My question is: how do you restrict or disable the field TYPE so that either you can only choose some types of parents and not all, or search for only one pre-selected type?
That TYPE field is merely a filter to allow you to more easily narrow down which artifact you're looking for. Unfortunately, it can't be restricted or disabled as it is driven by the object model and how artifact relationships are designed in Rally.
For example, User Stories are allowed to be parented to either Features or other User Stories. This is why you see both of those options in the dropdown. But in the case of Features, they are only allowed to be parented to Capabilities. Since there is only one parent type available, the field is automatically disabled because you have no choice.
Another example is Tasks. They can be assigned to User Stories, Defects, Defect Suites, or Test Sets. In this case, you'll see all 4 of these options in the type filter dropdown.
And again, these relationships are inherent to Rally's core design and therefore cannot be manipulated or disabled.
