Let me start from the last question.
You can use a simple numeric slide; right click on it and select 'Text labels': it changes to a slide with only two options (max and min or something similar) with a text display with the up/down arrow keys. Right clicking on the text displays, you will find options for adding or deleting or even enabling/disabling items in the 'ring'. Once you terminate creating your list of items, you can hide the text display to have a control more similar to a ring. The control remains a numeric one.
Now to come to the first question: if your vi uses a control like this, you must display the text display, select on it the items you don't need and remove them.
NOTE: if you remove an item in the middle of the list, all subsequent item
s will be shifted one place back, so the numeric value associated with each of them will change and this will affect the behaviour of the vi (you will have to adapt a case wired to that control to the new situation of the list, for example). You could consider simply disabling the items you don't need...
Roberto