Why do you care? If you use READ to get the value back I'd be very surprised if it read in the wrong byte order.
Anyway, I don't know of any DEFINE or anything to change it so, if you really need reverse the byte order, I'd probably try something like:
Code:
Value VAR WORD
temp VAR WORD

Value = $1234  ' Some value

temp.lowByte = Value.HighByte
temp.highByte = Value.LowByte

' temp is now $3412

WRITE 0, WORD temp
/Henrik.