Would your edit invalidate existing answers?
Go ahead and edit your question.
Post a new question - but make sure that you state exactly why that change makes the question different and why you expect the answers to be different from the answers to the first question so that it won't get closed as a duplicate. It's always a good idea to link to your old question in the beginning of the new one and explain what's different. You can also incorporate what you learned from the answers in the old question to show how you adapted the new one.
I am not sure
Refer to your question specifically on Meta by mentioning it in the meta post.
I am not sure if the new question would be viewed as a duplicate
Preferrably post your question in the Sandbox that is designed for situations where you are not sure whether a question would be on-topic. Checking whether a new question would be regarded as a duplicate is a normal thing for the Sandbox.