Can I Request Presenting a Different Paper at a Conference? Important note: This is for a humanities conference.

About a month out from a conference, I realize that the abstract I wrote is not going to work. I can write the paper I set out to write in the abstract, but it's not going well due to archival limitations. I have received a small stipend to attend this conference, so I feel obliged to go. In addition, it is an important, international conference and I have already booked flights. I am a PhD Candidate on the job market, so I would like to "look good" around people who could very likely be on my hiring committee someday.

Question: At this point out, I'd feel more comfortable presenting on an entirely new topic. The new topic would be in keeping with the topic of the panel. I am embarassed to ask the panel organizers if I can submit a paper on the new topic. I mean, I should know better, right? However, the new topic is still related to the overall theme of the panel. If they say "no," then I imagine that I will still need to go ahead with the original abstract. How do I make this request without sounding like an idiotic grad student?

I don't want to offend anyone by changing my topic, but I also don't want to offend anyone on the panel by presenting a paper that isn't going to be great.
At humanities conferences it is normal for people to give papers that are nearly unrelated to the abstracts that they submit. Few people who change their paper topic bother to notify anyone about it. I admit that I've done this a few times. It would certainly be polite to notify them that you are going to speak about something different, but there's no need to feel bad about it or be apologetic. This is a normal thing. No one will mind. 

As an aside, you'll soon notice that many senior academics provide extremely vague abstracts to conferences. This is because they don't know what they want to talk about, won't know until they make their presentation on the plane there, and want to leave their options open.