INT 1A - SNAP.EXE 3.2+ - "SNAP_SETANCHOR"
        AX = 7002h
        STACK:  WORD    anchor number (0000h-0009h)
                WORD    new value for the anchor
Return: AX = status
            0000h successful
            FFFFh failed (top word on stack not in range 00h-09h)
        STACK unchanged