Chadi,
Why wouldn't you use the ID field for this custom text? The ID is easily called in the schedule and you can be filling it in in the Info box as you work?
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"