A Tweecer is the only way you can change the calibration without changing the maf. Other then that the MAF will have to be recalibrated for 24# injectors.
from what i understand the 24's are not going to affect ur car to bad, if u dont change the MAF, u will run a tad richer at idle but will run good at WOT. i sound dumb saying this but i ran my car that way for a while, and they still did the job, although to be honest u should wait till u absolutely need injectors and do them with a calibrated MAF at the same time.