Full Time to Part Time status is original signed off letter still legally binding?

I relocated to Raleigh to work at a Geotechnical Engineering firm last November. I received a relocation bonus to pay moving expenses and it states in my contract that I would have to repay the bonus should I leave before 12 months. This week I was offered an employment transfer within the same company to a part time position with the same title, job description, etc. So, my "hourly" rate of pay is the same, but I am only working 30 hours a week. The relocation bonus was not mentioned in this offer. If I am under this new job description and find a new job (which I may have and it is more likely I will get it if I go immediately), am I still bound under the original offer to repay the bonus?