The Product Owner is the absolute owner of the Product Backlog. As such, he/she has the last word on what goes in, stays in, or gets out of it.
I wouldn't recommend to keep stories in the backlog "just in case." True, there is a cost associated with creating a story, but each item in the backlog will have to be maintained, reviewed, reprioritized, etc. and that represents a cost as well (in lean thinking, it's "inventory", and considered a waste.) I'll argue that the cognitive load of all that work is significantly higher than the creation cost (unless, of course, a lot of effort is spent specifying and detailing the work items, but that's a separate problem in itself.) Ultimately, if something is important enough, it will come back at the appropriate time.
All that being said, it's possible that in your particular situation you might feel that, as a PO, you don't have the final authority to remove items from your Product Backlog. Many organizations declare their Business Analysts to be Product Owners, but they don't give them full authority over the Backlog (and the project in general.) If that's your situation, then think who in your project organization has that final say about what goes in and out of the backlog, who can decide on the project direction, who is the "single throat to choke" if the project goes south; that person is really the Product Owner.