Which means you have a serious conceptual issue. You should take care of that when you import the data in the first place.
Quite so.
I have several custom informats depending on the project that turn various text strings such as N/A, UNK, or "(NO DATA)" and "(NOTHING ENTERED)" to missing, or "special missing" as needed, when reading the files.
Fun. Write a macro then that does it for one data set and then call it for all. You can use _character_ to reference all the character variables in a data set and use an array loop to set it.