I have 1 application page project and it is deployed. Now I want to make a change to it and deploy it somewhere else (same server and site) without retracting the currently deployed one. From one application page project I want two separate deployments. How do I do this? Having looked in the project properties I do not see any way to change that. I know that it has to be deployed to layouts, as with all application pages, and I tried deploying after changing its name but it still retracted the existing application page.
Application Pages are deployed to the server hard drive in one place for the whole farm. This means you cannot deploy the same page in the same location without affecting the previous deployment.
You would need to create a separate solution that deploys it in a different location (i.e. a different folder within /_layouts).