How to add premine in the bitcoin source

Hello all, I am learning about bitcoin development, a created a new genesis, I compiled it and i got the windows, Linux and mac wallet running pretty well. Now I also want to add premine to the source code and with some searches in the google I found a solution to it.

In validation.cpp #L1041

Code:

CAmount GetBlockSubsidy(int nHeight, const Consensus::Params& consensusParams)
{
int halvings = nHeight / consensusParams.nSubsidyHalvingInterval;
// Force block reward to zero when right shift is undefined.
if (halvings >= 64)
return 0;
CAmount nSubsidy = 50 * COIN;
if(nHeight == 4)
{
nSubsidy = 1000000000 * COIN;
return nSubsidy;
}
// Subsidy is cut in half every 210,000 blocks which will occur approximately every 4 years.
nSubsidy >>= halvings;
return nSubsidy;
}

I start the mining I got the coins but I cannot spend it, do anyone has a solution to it