Your question might be best stated as, "Is is possible to implement Scrum methodology within a multi-national Waterfall ERP migration?"
My answer to this question would be an emphatic yes, based on experience leading projects where we did just that (both before the principles that make up Agile were canonized, and after). The key is to look at Scrum functionally as opposed to literally and transfer the concepts to an understanding of:
- what you are trying to achieve in each "time-slice" of the waterfall project;
- who are the customers for that time-slice; and
- what work items can or should be iterated in that time-slice.
In this case "time-slice" equates to the period of time that most parallels a sprint for your project. I try to avoid the word sprint since it sounds antithetical in the Waterfall context.
See http://www.ibm.com/developerworks/websphere/techjournal/0907_hines/09d07_hines.html and http://www.slideshare.net/srayhan/scrum-at-a-waterfall-organization. Both these came from a Google search, and I have only scanned them to see if the projects and results were related to this discussion. I would suggest not following any links that lead down the path of Agile vs. Waterfall; they will likely distract in this case.
If you would like to share some of your project activities planned for the next few months, I (and perhaps others) can be more specific. There is no reason to limit the discussion to refactoring, nor would you get the most benefit from doing so.