Personally I wouldn't attempt at resharpening replacable blades either on expandables or fixed blade heads. I don't feel the replacement costs are too high for the sharpness quality. Unless your extremely talented and there may be a few, you won't get them as sharp as they should be. IMO.

Stock up on new replacements and use the used blades for practice.

The rule I like to follow is "One shot and the blades are done for hunting purposes. "