The drop downs of Selection fields like oppo_priority come from sets of translations. 

Have you seen:  https://www.sagecity.com/sage-global-solutions/sage-crm/b/sage-crm-hints-tips-and-tricks/posts/working-with-selection-lists

Thanks Jeff. But only doubt is next time a user adds new option it will not be synced with the lookup we create for each option, right?

If you only want to filter on load, in the createscript you can use the RemoveLookup function. I think it's called that. It's been a while since I did scripting

But how often is a new option being added?  Are these dynamic selection lists?  Do you have lots of users with rights to change selection list options?

New options are added quite often based on their requirements. Not many users have the privilege to add new options.

Yes these are dynamic selection lists. In the summary, a script is added on the custom content so that when case type changes it will automatically change the options list in the case category field.

We would like to do the same in the workflow stage also.

Same here I've done this two ways, the 'RemoveLookup' option - which with workflow is straightforward as you don't even need to worry about doing IF / ELSE clauses. (this works well if you're just wanting to remove a handful of items, any more an it becomes a bit of a maintenance headache) 

Secondly I have created 'dummy' selection lists and then within the Workflow via script 'changed' the Lookup Family for a selection field so it suddenly references a completely different list (so one master with all values (which is the true Lookup Family) and then 'sub lists' which only have values that suit the different scenarios - whilst it needs a little work to maintain, it works well for big lists)

Thanks for the response

Thanks for the ideas.