As of SERVER-91123, the config fuzzer supports changing runtime-settable server parameters periodically during test execution. Editing config_fuzzer_limits.py allows you to specify a server parameter to runtime-fuzz, including how a value for the parameter should be chosen and how often to change the value. More details can be found in that file and the provided ticket. 

Please add cluster scalability-related parameters that would be good to fuzz at runtime to this configuration.