I have a App in my Azure, but I have to change it to another Azure (my client one) who it's already running with another url. The App have several App Parts already being used in a Sharepoint Online Web Site, at least 100 pages using it, so I don't wanna have create a new App Identity, delete and add in every page. There is a way of change the App Url I registered keeping the Secret and the Id?
You will need to update your app with the new url and redeploy to the App Catalog. Make sure you increment the internal version number in the manifest.
After you do that, a job will run (it might take up to 24 hours) and the site admins in each site will see that an update is available on the app. When viewing the app in All Site Content the app tile will display a message saying an update is available and will provide a button to get it.
Once the site admin does that he will be prompted to trust the app again, and the update will install. This process will have to be repeated for every site that has the app. There may be a way to script this process, but I don't know what it is. If you have a lot of sites you might want to look into that.
So in summary, you do not need to generate a new client ID and secret, but there is some manual effort involved.