Trying to switch to anesthesia during your prelim year will be more difficult that matching outright because there are fewer spots available. Some programs have spots open, but the number is substantially less. The other option is to reapply through the match and figure out what to do with that extra year you would have to wait.
Another option would be to do a pediatrics prelim year. MCW offers one, and other institutions may also. It would likely be easier to do the peds prelim year and then choose to stay in peds than start a peds residency and get an anesthesia spot at a good program outside the match. I know I could have easily stayed in internal medicine after my internship had I chosen to do so.
The best option is to figure out now what you want to do. I'd suggest an anesthesia rotation with a little time in peds anesthesia (not a ton because you won't get to do as much, but enough to see if you like it), if that's what really interests you, and a NICU rotation.
The ACGME web site has info regarding the clinical base year (internship).
"At least 6 months of the CBY rotations must include experience in
caring for inpatients in internal medicine, pediatrics, surgery, or
any of the surgical specialties, obstetrics and gynecology,
neurology, family medicine, or any combination of these. In
addition, there should be rotations in critical care and emergency
medicine, with at least one month, but no more than two months,
devoted to each. Up to one month may be taken in anesthesiology.
Rotations should ensure continuity of teaching and clinical
experience. Each month of training may be counted only once.
For example, a rotation in a pediatric intensive care unit may count
as either a month in pediatrics or a month in critical care medicine."