Tough to answer because I don't know what you're entering in the MA field currently. If you're entering a 5-digit MA code, and the source of that data is in line with the appendix to HMDA-Getting It Right for 2004, you're most likely OK.
If, though, you're entering a 4-digit MA code (not even sure if your data entry software will allow that), then you can expect to re-enter.
I'm in Michigan, and we lend in maybe a dozen counties on the west side of the state. We built a conversion table based on county code, using the 2004 Getting It Right guide. Data entry staff know which county results in what MA code - I'm not expecting any re-entry issues from this.
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Opinions are Bartman's, not those of my employer. "A noble spirit embiggens the smallest man."