The env variables are used and defined based on the environment dev, test and production etc . These values does not change frequently and can be changed from ProcessAdmin -->Installed app --> Environment Variable tabs. Once changes , it will be changed immediately. The ENV values can be changed by Admin Group only.
The EPV can be searched and changed using ProcessAdmin -->Server Admin --> Admin Tools --> EPV. EPV Value changes can be scheduled using the tool. and It will be effective on the specified time . EPV are exposed to certain group and group member also can change the EPV value .