Bitcoin code 390

M9 1a8 8 0 1 0 0 16A8 8 bitcoin code 390 0 0 9 1zm. Can I change bitcoin core code for my node?

Bitcoin is working on some of sort of code. Now it is p2p network as well. When I am accessing network as a full node, I have to download the whole ledger first and then I can proceed. Where does the code comes in picture? Do I download bitcoin core code as well with the ledger?

Also, Can I access the network if I have made some changes to the code. Say, I have changed the value of the BTC rewarded for mining, and then accessing the network, to get increased reward. Next time try to raise separate questions please. And yes, there is a p2p network to excahneg information about valid transactions and valid blocks.