As a general rule, when you make changes to a logical file, which causes a change to the level identifier (for example, adding a new field, deleting a field, or changing the length of a field), it is strongly recommended that you recompile the program that uses the logical file.
Sometimes you can make changes to a logical file, which changes the level identifier and does not require you to recompile your program (for example, adding a field that will not be used by your program to the end of the file). However, in those situations you are forced to turn off level checking to run your program that uses the changed file. That is not the preferred method of operating. It increases the chances of incorrect data in the future.
To avoid recompiling, you can keep the current logical file (unchanged) and create a new logical file with the added field. Your program refers to the old file, which still exists.
You can use the Change Logical File (CHGLF) command to change most of the attributes of a logical file and its members that were specified on the Create Logical File (CRTLF) command.