I have READ about the process.
If the Berdan pocket is smaller than a large Boxer, the case can be dropped over a steel rod in a vise or heavy base and a hammer and punch used to bash down the Berdan anvil, mostly closing the flashholes in the process. Then the right size endmill will smooth out the bottom of the pocket and bring it to the right size for a Boxer primer. Drill a centered flashhole.
If the Berdan pocket is larger than .210 (there are a lot of .254s) repeat the process except you have to lathe turn some teeny little bushings to take standard Boxers. (Freedom Arms offered large-to-small primer pocket bushings back when they were changing from large pistol to small rifle primers for the .454 Casull, so it can be done safely.)
For black powder cartridges, it has been done to bore and counterbore a hole to take the whole head of something like a .32-20 or .22 Hornet which is then low temperature soft soldered or Loctited in place. Or just bore to take a shotshell battery cup primer. Either of those is for black powder or very light smokeless loads when there is no other way to get the old gun shooting at all.
Any of the above is a tremendous amount of work, something to do for a very odd caliber you cannot get Boxer brass for or even the right size Berdan primer (which are scarcer than they used to be.) Not something to do to make use of Slobovvian surplus 8mm or some such.