I'm going to guess that you tried something like:
if var=1 then var='yes';
This will not work because the variable VAR is numeric and can not hold character values.
To add to @Rick_SAS's suggestion: Formats are very flexible. You could have multiple formats that assign different values to 1/0 and use as needed. Such as True/False Answered/Not Answered. You could even provide more information such as "Has insurance"/"Does not have insurance", without adding any variable just using a different format for use in a procedure.
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