In the CoreSettings.config file you may noticed some settings that uses "upgradeif" setting. For example:
<customSetting key="MaxConcurrentSlowMsgsThreadPoolSize" type="local" value="4" upgradeIf="gt" />

upgradeif indicates if a core setting will be updated during upgrade (by default settings are not upgraded, only new ones will be inserted).

There is 3 options now:

gt – the setting will be updated to new value if old value is greater than new

lt – the setting will be updated to new value if old value is less than new

ne – the setting will be updated to new value if old value does not equal to new

Example:
“gt” means that our value will take over the customer’s if its greater than it, i.e. if there was a value of “2” previously, but our new one is “4” in 7.5 with this option – we will override. But if customer set it to 10 before, and ours only 4 – we will not change.