Huh. As I egosurfed, I found this
PennMUSH change log:
+ Version 1.6.9 patchlevel 1 September 26, 1996
+
+ New Function:
+
+ * setr() is like setq() but returns the string as well.
+ It's identical to [setq(#,string)]%q#. Suggested by Adam Dray.
I only vaguely remember discussing this with someone on the PennMUSH team. I think TinyMUSH copied the concept of setr() from PennMUSH, not the other way around. Maybe David or Lydia can tell me, not that it's that important.