Dan,
Seems like you might have two questions.
First, if you want to change the standard assignment to a standard with F in it, you can uses the Standards Assignment button in Acquire! (during setup of sample) or in Analyze!
Second, you can add, modify, duplicate , delete, search etc Standard compositional information using the Standard.exe application (In the same folder as the other PFE applications). If you need to modify a standard composition that has been used by others in the past, you might consider duplicating the standard with a new number, and making the modifications to the duplicate entry; this way the original composition still exists for people to use, should they need to. FYI, If an older .mdb is opened with PFE and there are inconsistencies between the composition stored in the working database and the standard.mdb, you will be prompted, and asked how to proceed.
Gareth