Difference between the Debug class and Trace class
The Systems.Diagnostics namespace includes Trace and Debug classes and both have very similar methods. The primary difference is that calls to the Debug class are typically only included in Debug build and Trace are included in Debug build and Release build. Moreover, we can say that Debug is used at the time of application development, while Trace option is used at the application deployment when any errors will be traced and will be written to log files.
Is it possible to change the value of a variable during execution time ?
Yes. In Visual Studio, there is the command/immediate window (when debugging, under the Debug -> Windows menu) which allows you to change variable values.
What is the difference between a Debug and Release build ?
Generally debug builds are not optimized and contain debugging symbols, while the code built in "Release" mode will be optimised for speed or size and also will have all the information used for debugging removed.
Related.....Difference between a Debug and Release build