Library parts that are AC11 specific will show up as dots.
Using find and select to click on one dot, get its name, select all of that one and then navigate with them selected to the AC10 version takes not that much time for each different library part.
If you have favorites in the AC10 file that match what you had in AC11 you selected, ( all the tubs for example) then you can double-click on the appropriate favorite and it will take on the favorites attributes and parameters.
You will need to reset all the sizes, materials, pens etc for each object or set of matching objects. If you created custom library parts, then you will have to recreate them from the slabs or whatever else you used to make them.
Hopefully you kept them in your file.
More tedious then difficult.
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"