Maybe photo your existing mars mech for clearer advice but as said above you need one which it is possible to reprogram to a desired token.. some already receive a selection of commonly used tokens as well as uk coins (selectable by internal jumper links a b c d e in various combinations if you have those token types brass, steel, chrome over brass , steel magnetic , alloy ,etc so many other types and size value)
Links visible behind side panel on selected type mars mechs usually fitted to 1990s machines onward (older ones less likely to be reprogrammable)
If you have a stock of tokens already you can send the mech with a few tokens (if it’s one which can be upgraded) to Maggi electronics Bolton include about 10 of your own tokens . Explain that you want it to accept those for particular value pulse to your current credit board ( eg as token 20p? 0r instead of 50p or pound ?
They also sell bulk tokens of their own several styles or designs but will program the mech for around £35 (estimate may be out of date since I last used them)
Or phone swallow amusemts look at his website mechs front entry front return are about 35 quid plus vat for a replacement ask if he can program it to a particular token… I think he also sells tokens
There are so many types available but to be programmable they must have the self teach faculty or be fitted with the EAROM 82s126n or 82s129 82s130 visible in the mech when you remove the side reject route panel secured by one positive screw and can be cleaned with a dry or slightly damp (water) while it’s off - never ever use polish or any lubricant on a mars mech - that kills them very often.
Hope that helps - my advice tho - if it’s not broken and for home use just stock up a few standard circulation coins and recycle them as you can get them out of the cash box as required ( moral of this tale “ if it ain’t broke don’t mess about trying to fix or change it! “ )
EAROM electrically alterable read only memory ic 16 legs can often be used twice ( lifting out pin 15) or thereafter replaced and programmed to desired tolerances using a mars programmer.
Be careful buying off eBay as mars mechs can have different mounting pins which are actually removable if you have the mech knowledge but the important thing is front entry front return if your current mech is missing .
Caution there are odd versions of the 126 which can’t be upgraded but I won’t bore you with too many details just beware!