If you are an editor of the deck, but still are asked to create a new revision, that means that the deck is used in some other place. What you can do in this case in order not to create a new revision for the whole deck is:
Right-click on the parent deck for the slide (not a root one, but the parent of this certain slide)
Choose "Open in a new window"
Go to the Edit tab of this small deck opened
Click "Create copy and save" on the bottom of the page
Return to the previous "large" deck
Update the page. Now if the "small" deck is selected, you will see a yellow exclamation mark, indicating that a new revision is appeared.
Go to the History tab, and click "use this revision" near the upper revision (which you've just created)