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(RESOLVED) Is a new complete installation needed when modifying code?

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I installed WRF4.2 following the instructions given at I would now also like to have a WRF4.2_2 that will include a few modifications in files /dyn_em/module_big_step_utilities_em.F, /dyn_em/module_initialize_ideal.F and /phys/module_fdda_psufddagd.F. I wish to keep the original 4.2 version. Do I need to repeat the whole installation procedure for WRF4.2_2 ? Or can I take advantage of the already existing WRF4.2 structure ? May be with a few simple steps I can setup a /run_2 directory that incorporates the few modifications in the above 3 files ? The default version would be used from /run and the modified version from /run_2. I would very much appreciate if you could let me know how this works.
If you want to have both installations, but don't want to fully recompile the code, I would suggest making a copy of the unmodified code to its own directory. Then inside that directory, make your modifications, then recompile the code in that new directory. Since you are not modifying the registry files, this will not require a "full" compile and recompiling should be much quicker than a new compile. You don't need to issue a "clean -a" or reconfigure. Just simply compile.