Difference between a re-grind and re-tip?
A re-grind is the term used when the existing tipping point of a nib is as broader or broader than the desired end result of customization. For example, a pen can be re-ground from a Medium to Medium Stub because the customization is for a tip of the same width. A pen can also be reground from a Medium to a Fine or Extra Fine point, because the request is to go from a Medium tip to something smaller.
A re-tip is necessary when the existing tipping is not as broad as that which is desired. For example, a customer would like to go from a Medium to a Broad or wider nib. In cases such as this, the existing tipping has to be physically removed and a new pellet must be welded onto the tines to accommodate the new tip. Any broader customization will require a re-tip.