Manipulatie game Eprom from old Guilder to Euro

Ik have different physical old fruit machines from the Guilder period. 1 Guilder coin is 4 credits, 1 Rijksdaalder is 10 credits. I would like to manipulatie the Eproms so that 1 Euro coin is 5 credits and 2 Euro coin is 10 credits. The 1 Euro coin will drop in the Guilder pipe and the 2 Euro coin in the Rijksdaalder pipe. Basically I'm only looking tot manipulate the program in the Eprom to change the value for 1 Guilder/Euro coin to 5 credits instead of 4 and to also change this for the pay-out.
Is the any experience with this and are there suggestions where to find this settings in the HEX Eprom files?