Steps for removing the key fields on a physical looks fine.
But, The approach will be difficult and it may need lot of effort if we proceed as per these steps.
And, this complexity is based the number of programs the file is using. Because, You will need to change all these programs(not just changing the F spec and Recompiling).
You can have a look at the process suggested by “Yorkshireman”
You can Rename the physical file and modify it by removing Key fields, and have a Logical File with the name of initial PF.
and then, Find out all the programs which are using the File.
There maybe no need to change the F – Spec, it just Requires Recompilation of all the Related programs for having the File Identifier of LF.
I suggest, not to have Key fields for Physical File.
You can have LF with the required Key fields.
The advantage of having this approach is, In future if we get a new program which needs to use the same file but with different Key fields combination, There will be need of re-compiling all the programs associated with that PF.