static const CAmount MAX_MONEY = 21000000 * COIN;
I heard that Bitcoin is limited to 64 bits internally, which limits the number of supply. 21000000 is a lot more when stored in satoshi. Is there a technical limit in the number of supply if I clone Bitcoin core and for example change chainparams.cpp to deliver 10x time more coin than the original bitcoin?
That's the technical limit for the maximum amount of the smallest unit you could reliably transfer:
https://en.wikipedia.org/wiki/9,223,372,036,854,775,807
Beyond this number you'll get an overflow. Bitcoin having a max final supply of roughly 2,100,000,000,000,000 Satoshis leaves some wiggle room for increasing the coin supply on clones (alternatively one could also increase the perceived coin supply by reducing the number of digits).