Mower tyres are usually listed as Overall Diameter x Rim Diameter x tread width
So I don't think a 12" diameter tubeless tyre will fit on a 10" diameter rim and make a particularly good seal
Some times you can luck it in and get some bigger rims that will bolt on your axel but usually bigger rims have a different bolt pattern or spacing to prevent owners overloading the transmission with bigger rims then making a warranty claim.