Can we use AWS SDK ECS client API in production environment

Yes, you can, but it is NOT recommended. If you do, MAKE SURE that you update the CloudFormation Stack shortly after with the correct config to put your environment back in sync.

I would recommend you do it using CloudFormation. Take a ChangeSet and ensure the service is not being recreated (your change should not cause this, but if you already have a drift, it might happen). If the Sevice is replaced, you can expect a 2-7 min hiccup so maybe do it off hours.

Hope it helps!

Making modifications outside of Cloudformation (or any IaC) will result in drift. If you don't make the same modification in your CF yaml file, the next time you run your CFT, it will reset the parameters. In many organizations, no changes are allowed without using IaC. That is a good practice as allowing direct modifications in production is a recipe for disaster and can cause differences in the environments between production and lower environments. You will never know what you tested in the lower environments will work in production.