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restart run with different namelist value

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I have a WRF simulation with very tough initial conditions over complex topography which requires a given time_step_sound value to avoid instability. As a consequence the computation time gets very long. To improve efficiency it would be fine if I could after some time use the default namelist value. So, can I run an initial stage with a given time_step_sound value, stop some hours later and then restart with a shorter time_step_sound value ? In general, are there any namelist parameters that can be modified in a restart run or none of them ?
I just tested this out using a quick/basic test and while the model does not fail when you use a different time_step with a restart, you do get different results than you would get if you kept the time_step the same. This probably isn't problematic and the results likely wouldn't be unreasonable - they would just differ slightly because of the difference in calculation times. You could test this out - running a short test or two to make sure you are still seeing reasonable results if you do this.
Thank you for your explanation. I meant the time_step_sound instead of the time_step value but your reply is encouraging. I will test both types of parameter modifications and I will let you know if I arrive to firm conclusions.