@ronjonp
If I understood correctly, when using BricsCAD you must go through (entupd (cdr (assoc -1 (entmod (subst (cons 8 "Layername") (assoc 8 entdata) entdata))))), and in AutoCAD you can do it through (append) like you showed... Anyway the best is that you make sure it works for both AutoCAD and BricsCAD, and that is by using (subst) method...