Manage Environment Variables - CI/CD - Cloud Foundry MTA Deployments

I would appreciate some guidance/ pointers to some resources on this issue I am facing.

In my SAP trial Cloud Foundry environment I have configured a CI/CD pipeline using AzureDevOps. I have been able to configure the build and deployments stages for the master branch which points to a production environment. This is a UI5 application and the deployment is done as an MTA.

I wish to expand this pipeline to work across different branches i.e. I wish to have two other branches for development and testing and have these pipelines deploy the app to the corresponding development and testing branches.

What I need help with is setting up environment variables for each environment in each branch. What is the best way to do this for MTAs?

For starters, I would like to have environment specific app names and environment specific data sources for my app. This can be done my modifying the manifest.json in my application, is there a way to refer an environment specific manifest.json file for each branch? i.e. dev-manifest.json , test-manifest.json or prod-manifest.json

Can a similar thing be done to modify the mta.yaml based on the branch that is being built?

This is the kind of app I am dealing with for your reference; https://github.com/MFredX/sap-btp-ci-cd

Thank you.