Hi,You can try delete existing fields (arpcy.DeleteField_management) from copied featureclass, then adding your attributes (arcpy.AddField_management), putting new values with arcpy.CalculateField_management, and at last appending to existing featureclass (arcpy.Append_management). So it will look something like:
arcpy.CopyFeatures_management(lyr, tmp_fc)
f_list = arcpy.ListFields(tmp_fc)
for f in f_list:
if f.type not in ('OID', 'Geometry'):
arcpy.DeleteField_management(tmp_fc, f) #delete all fields except of geometry and FID
arcpy.AddField_management(tmp_fc, field1, 'TEXT')
arcpy.AddField_management(tmp_fc, field2, 'LONG') # adding fields you need
...
arcpy.CalculateField_management(tmp_fc, filed1, value1)
arcpy.CalculateField_management(tmp_fc, filed2, value2)
...
arcpy.Append_management(tmp_fc, out_fc, *params)
Hope it helps.RegardsArek