From what you have said, I am thinking that the added white/cream is more so bordering the main part of your quilt top. Thus would not be that hard to remove and switch in the new whiter one?
I am one who is of the mind that it is better to take the time and switch things while I still can. Usually those early gut feelings are bang on!! So I might as well listen to it, as later, I will just hate it .... and hide the quilt! Why do all the work, if ?????????
My suggestion would be to lay your quilt top on top of a bed, or floor.
Then overlay your new white onto the parts you are replacing.
Then walk away.
Periodically come back, for what I call that "quick glance" .... often times to me, it is those quick unexpected looks at something (like this) that tell me whether it is the "right" match, or not. Whereas, if I "study" it, I start second guessing myself............
I am doing that right now with a border candidate. I have it on the wall of my office, and when I walk in, I have forgotten about it, and the first, quick glance, lets me see it fresh and somewhat unexpectedly. Yes, I think it is the one!
Good Luck!