You should talk to your letter writers about this. Ideally, they write you different letters for different programs. Usually letter writers write the letters that are very specific when it comes to you and your details but quite generally when it comes to the "addressee". So, it should just be a matter of find/replace the field names and school names.
Find out how your letter writers would like to know the information. For me, I had a table of school names, deadlines and dept name (some were field1 some were field2). This helped them keep track of how to "address" each letter.
