Then you perform the experiment exactly* how you said you would based on the pre-registration, and you get to publish your results whether they are positive or negative.
* Changes are allowed, but must be explicitly called out and a valid reason given.
I take it you don’t do research. Cause boring is nothing compared to wasting month of time and money only to get a negative result that nobody will publish.
I have a broad and open-ended focus, I work as usual on the things I find interesting, then sometimes I see a thing that looks interesting and decide to investigate, then sometimes my initial tests give good results, but more often then they don't, but they give me an idea to do something completely different, and some iterations later I have a result.
I imagine that depends on a field of research. IT is cheap, but I imagine a physicist who wants to do an experiment must secure a funding first, because otherwise it's impossible to do anything. And it requires one to commit to a single topic of research.
That part is true in all fields. And one of the things that pre-registration enables is the publishing of those negative results.
Otherwise, once you're done the research and got the negative result nobody wants to publish it (unless it’s very flashy). Without being able to publish negative results, and therefore read about them, each researcher must conduct an experiment already known, if only in private, to not work.
People will still want to do their own exploring to get a feel for a problem.