"Replace with sequential dataset" - what does this mean? Do you want to eliminate the use of the INPUT/INFORMAT $FEIN and change the SAS code to somehow take the possible input/output data-values and maintain then in a sequential file?
And, if so, would you expect your SAS program to read the sequential file with each execution, take the current data-values and generate your SAS statements to perform the data translation?
Have you looked at PROC FORMAT and CNTLIN= where you would have a DATA step to read your external (sequential) file and generate the SAS-required variables needed to use PROC FORMAT and input your equivalent INVALUE parameters from a SAS file?
Suggest reviewing the SAS DOC for PROC FORMAT (not having to do with z/OS specifically, other than reading / inputting your external file).
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You are correct in your assumptions - the sequential dataset IS intended to replace the hard-coded values. I have not worked with PROC FORMAT before, but I will give your suggestion a try and let you know how it works. Your help is greatly appreciated - I know only a little SAS, so did not know where to even start looking for the answer..