I'm going to a conference in December and I will have a 20 minute talk there. Originally, a colleague of mine was supposed to go, but personal circumstances resulted in my taking part instead. My colleague and I cover the same area, so this is not the problem. But since my colleague handed in the title of the talk we have reevaluated our use of field-specific key words. Therefore, I think the title as it stands is a little misleading. Is it common practice to adapt conference presentation titles? I found one topic covering a similar matter, but it hasn't got much attention.
Given that, officially at least, the title of your talk will still be the old misleading one, I'm not sure how much there really is to be gained by changing the wording of your first slide, which seems to be effectively what you're thinking of doing. In fact, having a title for your talk that doesn't match what's in the programme could be potentially misleading anyway (for example, if the chair reads your title from the programme, rather than the slide, or if the title on the screen isn't what your audience had expected).
If you feel that your title is misleading then what I think I would do would be to begin the talk by making it clear that the title is potentially misleading, and then clarifying what the talk is actually about. You could even, before the audience's eyes, swap your old title for a new title.
As long as the programme has the old title then to a certain extent the damage is done. I think the best approach to take is simply to make clear from the outset that the title is misleading, and explain what you're really going to talk about.
It is quite normal that in a conference with 40 talks, several speakers change the titles of their talk on the spot. Common reasons are that there was some success after registration, or during the preparation of the talk the speaker found out that he cannot cover everything in the prescribed time. Sometimes it happens that a mistake was found to late, so the content of the talk has to be changed substantially. Usually this is not a problem.
However, people either come to your talk because they are attracted by the title, or because they just want to appear polite. It would be unfair against the former if you change the content of your talk, in particular if there are parallel sessions. So if after submitting your title and abstract you find some much more interesting results on some other topic, you should still stick to your original talk.