When you say add it at the end, you mean compile it back in?
Yes. As GBT expects coinbase aux, you can just include it as an empty field again. It'll be easier to ensure minimal downtime as you won't have to waste your time to manage each of your mining instances. Alternatively, remove it from your mining client so it doesn't throw an error.
I guess this is where I am confused at, if I want to solo mine against bitcoind, which is the way to go if I don't want to downgrade to 0.19.1? Add it back into the bitcoind code and recompile (not sure exactly how) --or-- remove code from miner client and recompile?
Thanks