Injecting Tezos proposals
Always inject responsibly. If your proposals wins, you're going to have to live with the outcome. Try your best to test and participate in the rest.
The Tezos protocol gets modified mostly by the developers working at https://gitlab.com/tezos/tezos. It's a collaboration of several developer organizations, which you can research by navigating through the contributor's names.
Once this happens, all you have to do is git checkout the repo where the proposal is finalized, sync a tezos node and inject.
In this scenario you will be contacted by a core dev who has composed a proposal outside of the main Gitlab repo (for whatever reason) and you are asked to inject the proposal because of your agreement with the parameters being changed.
In this scenario you will be contacted by a non-core dev group that has ample resources to work on the Tezos protocol competently. They will make sure all requisite testing is successful and they will write their own testing, in an honest effort to discover any issues within their code changes, no matter how small.