I have Anakee III on front and rear. However I doubt you'd have any problems with just changing the rear, especially if you stayed in the same general type and construction, (dual-sport type, radial construction). However if you purchase an Anakee III, I think you'd be even safer, being from the same manufacturer. I've always replaced just the tire that needed it, and often that's meant mixing older and newer models, and even mixing brands on some occasions. (PR2 + PR3, PR2 + Pirelli Angel ST, Even a Dunlop + Anakee).
Most of my bikes seemed to eat up rear tires much faster than front, however the DL650 has been much more even in tire wear.
Before my trip last year, I put the new Anakee III's on it because I was hoping to avoid tire problems during the whole 5-7000 miles I had planned. After about 7000 miles on them, they are still both in pretty good shape, and I'm expecting an unprecedented (for me), 10,000 out of them. (or more).
I have been very happy with the III's and I expect that my next set of tires will be these again.