Program in ILE-RPG (AS/400)

We have an existing ILE-RPG program. It reads records from one file (mainly) and according to hundreds of conditions (IF sentences) it fills certain value into field of the other file. Instead of these checks, we need to parametrise this: we will prepare one file. Chain has to be made to this file and value from found record should be written into the existing file. In the new file, we will have PK combined with more field. In first step program should search with all fields. If not found, it should search with blank last field. If not found it should search with last two fields blanked, … So, simple task for someone, who now ILE-RPG: input file declaration and few chains (if not found, chain again / if not found, chain again, …). We will also need explanation (education) of changes.