I don't think the curl pattern changes per se but I think what happens is over time (especially when people go on the whole natural hair journey) they learn to care for their hair in much better ways and as their hair grows it's growing in a much healthier state as opposed to when they used chemicals and/or regular heat tools on the hair. I think a lot of naturals that take care of their hair over time learn the moisture balance their hair needs which is incredibly important for optimal curl or kink defintion. So when you see their hair grow from short to longer lengths of course the hair appears to change or even if they keep it short and just take very good care of it..the overall look to the hair feels and looks different. The curls or kinks look healthier more defined and most likely hang much better.
But it's the same curl or kink pattern they were born with..it's just in a better state. A lot of naturals that utilize the Curly Girl Method report that over time. They can't get over how their hair looks so different..they have more curl or kink definition than they believed.
Also hair dye over time can change the look of curl pattern depending on what chemical dyes are is used on the hair and that in conjunction with proper care can really make a big diffence in the appearance of the hair. For a lot of people certain hair dyes actually help with frizz and the curls seem to come out a lot more defined. Henna can do this as well. Also a lot of "hold" products such as gel help with the "setting" of the curl pattern as it dries. Without it certain hair types can look very poofy and of frizzy. But I think what a person's natural curl or kink pattern is a genetic issue and pretty much a set deal.