Looking at cx_Parse + stuff, some thoughts and questions arise:

• Is it necessary to fiddle with the cache? Just undef _cache on perl side to enforce parameter changes; this ought to be a rare event? Stashing an opaque C struct avoids needless copying.
• Then what about unicode whitespace characters?
• quote_char, escape_char, etc., could be ints and default to -1 when undefined. Easier to test against. However ...
• Have you tried writing this thing as an fsm?

enum { TXT, BIN, WSPACE, UTF8, QUOT, ESC, SEP, CR, NL_EOLX, ..., NN };
enum { EXFIELD, INFIELD = 1*NN, INQUOT = 2*NN, CRSEEN = 3*NN } state;

while ((c = getc()) != EOF) {
    int ctype = cached->xlat[c];

    if () ... /* perhaps peel the most likely case(s) */
    switch (state + ctype) {
    case WSPACE: continue; /* nop: allow_whitespace test in xlat[] */
    case BIN: error(); /* again, resolved when constructing xlat[] */
    case TXT: state = INFIELD; putc(c); continue;
    case INFIELD+TXT: case INQUOT+TXT: case INQUOT+SEP: ... putc(c);
    ...
    case UTF8: case INFIELD+UTF8: ...accumulate/xlat...
    case CRSEEN+NL_EOLX: ...; state = 0; continue;
    case CRSEEN+...: error();
    default: error();
    }
    ...
[download]

Or possibly:

    enum { EXFIELD, INFIELD = 0x100, INQUOT = 0x200, CRS = 0x300 } sta
+te;
    ...
    int action = cached->xlat[state + c];
    decode(action);
    ...
[download]

Ultimately, the (handful of) UTF sequences may also be resolved by walking trie-like state tables.

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