with AC open , under the help menu, go to downloads. There find the AC10 migration library. This can be loaded in conjunction with the AC13 library.
Also you can always open a 10 file with only the AC10 library loaded. You do not have to use the AC13 library.
HTH
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"