You may have to look at the server source files in Subversion to find the relevant info, I'm afraid.
For the record, here are the 8 supported numerical values for the "fileAs" field:
Code:
52 /** "File as" setting: <code>Last, First</code> */
53 private static final int FA_LAST_C_FIRST = 1;
54 /** "File as" setting: <code>First Last</code> */
55 private static final int FA_FIRST_LAST = 2;
56 /** "File as" setting: <code>Company</code> */
57 private static final int FA_COMPANY = 3;
58 /** "File as" setting: <code>Last, First (Company)</code> */
59 private static final int FA_LAST_C_FIRST_COMPANY = 4;
60 /** "File as" setting: <code>First Last (Company)</code> */
61 private static final int FA_FIRST_LAST_COMPANY = 5;
62 /** "File as" setting: <code>Company (Last, First)</code> */
63 private static final int FA_COMPANY_LAST_C_FIRST = 6;
64 /** "File as" setting: <code>Company (First Last)</code> */
65 private static final int FA_COMPANY_FIRST_LAST = 7;
66 /** "File as" setting: <i>[explicitly specified "file as" string]</i> */
67 private static final int FA_EXPLICIT = 8;
So to switch a contact to "First Last (Company)", just set its "fileAs" value to 5 and the server will recalculate the rest.
(Note that the web client may not support value FA_EXPLICIT yet; this type of "fileAs" is not completely numeric but instead looks like "8:foo bar baz".)