Some solace and empty, unnecessary response if I may. Nah I don't know about the structural location of or access to Alias, but seems when adding to a Table of Contents (in Pro at least), the Alias is listed. Seems you are fine doing:
arcpy.Rename_management(fp_fcs_orig, fp_fcs_new)
# Now fp is renamed, so change alias on NEW fcs
arcpy.AlterAliasName(fp_fcs_new, 'new_feat_name')
...just not satisfied with the structure? Anyways - everytime I rename, I also AlterAliasName and now when adding FC to a map the proper name appears. In the example I gave, I renamed an FC and then proceeded to change alias to match.