Hi @wat,
I recommend not modifying the contracts in node_modules.
_From: https://docs.openzeppelin.com/contracts/3.x/#usage_
To keep your system secure, you should always use the installed code as-is, and neither copy-paste it from online sources, nor modify it yourself.
If you want to use a different version of Solidity, then you can install the appropriate version of OpenZeppelin Contracts.
Solidity 0.5
npm install @openzeppelin/contracts@2.5.1
Solidity 0.6
npm install @openzeppelin/contracts
Solidity 0.7
npm install @openzeppelin/contracts@solc-0.7
Also see: OpenZeppelin Contracts 3.3