If you want to provide a custom list of options, say in a drop down, you could do that as well using the listbox syntax
Example can be seen here - http://oriondemo.solarwinds.com/Orion/NCM/Resources/ConfigSnippets/EditConfigSnippet.aspx?SnippetId=7
.PARAMETER_LABEL @BGPAS
BGP Type
.PARAMETER_DESCRIPTION @BGPAS
Determine if you want to export Border Gateway Protocol.
.PARAMETER_DISPLAY_TYPE @BGPAS
listbox: 1=N/A|2=peer-as|3=origin-as