How can I configure special accounts in a private net

Algorand has 2 special accounts: Fee Sink and Rewards Pool.

How can I use this addresses in a private network? How can I configure it?

Also, one more question: if Rewards Pool is empty, then all participation addresses are not receiving any participation reward, right?

I am not sure this is the simplest way, but you can change all the genesis.json files (there are 3 of them if you used https://developer.algorand.org/tutorials/create-private-network: ~/net1/genesis.json, ~/net1/Primary/genesis.json, and ~/net1/Node/genesis.json) to specify different addresses for the fee sink and reward pool.

If the reward pool is empty at the end of a reward period (or at round 0), there will be no participation reward distributed at the next reward period.

Concretely, if the reward pool is empty at round 500,000, there will be no reward for the period 500,000-1,000,000. If you fund the reward pool during this time, participation rewards will be distributed in the next reward period 1,000,000-1,500,000.

Thanks @fabrice.
So essentially I will need to modify fees and rwd in the genesis.json file?
Is there a way that we can change these accounts in a runtime (I guess not)?

BTW: What’s the reason of having the copy of genesis file in ~/net1/genesis.json?

I think that it’s a staging file, that can be safely removed once the network creation is complete.
On any given network, the genesis.json files would always be identical on all the data directories. ( i.e. this is the “common truth” )