"Freshing' the barrel involves casting a lead lapp inside the bore on a rod, in a manner it can be adjusted for diameter (tapered spindle that is threaded on one end, then cutting a groove in the lapp for a cutter/scraper. Marking orientation, then, in a nutshell, running that lapp up and down the bore for each land scraping a new surface on each, as well as re-casting, and cutting each groove to a new surface.
Today, with today's barrel materials, much easier to re-barrel, or have someone like Ed Rayle re-bore and re-cut it for you.
Casting a lead lapp in the bore and lapping the bore with various grades of grinding compounds can also 'save' a barrel.
Taylor and I 'saved' a friend's custom rifle (built by Taylor) by doing this, using 2 lapps over 2 days, and about 8 total hours of work. Peter had always used boiling hot water as some writer said it was necessary and flash rusted his barrel every time he cleaned it. He was quite anal about having his barrel cleaned immediately after shooting and was always the first to have his rifle clean. He wouldn't even have a beer after shooting until he'd cleaned his barrel first.
The boiling hot water he used caused flash rusting every time, as soon as the wet patch was removed and before he could run a dry patch down the barrel, it would have dried and 'flash rusted' due to the barrel heat. continual flash rusting his barel over a period of 30 years use and it's bore was covered with fine pits, one end to the other. It was a horrid fouling gun with water based lubes like spit. The pits held onto fouling and although it didn't need to be wiped, loading was diffcult with the 3/8" to 1/4" tapered rod.
At least now after lapping, while not totally reguventated, it can be shot wit no wiping and easier loading with the rifle's tapered rod using our standard load practice, ie: 8oz (.020"denim) and a .395" ball, however his mould casts a .398 X .397" ball, which I have now for my .398" bore .40 cal. rifle. I use a slightly heavier patch yet in it's deep .010" rifling.