This is never a good idea when you are trying to remove heat between the seal faces. The special lubricant required to install the seal makes installation different than other seals. Any time something is different, errors occur. The rougher shaft finish requirement makes installation different also. The Buna N boot is sensitive to ozone attack once the package is opened, and people like to open packages.
Shops often have high levels of ozone caused by the sparking of electric motors.
The carbon face can be put in backwards. If it can be, it will be. The seal is not usually hydraulically balanced, limiting its pressure and speed capability. Unless the seal is on a cartridge you cannot make the initial impeller setting and other impeller adjustments when using open impeller pumps. The seal is limited to a replacement part, and with the great variety of materials specified you will have too many replacement seals in your inventory.